PHTHISIS HEREDITARY IN ANIMALS.

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disease to family predisposition, as the origin is probably endemic; but we must bear in mind, that this objection applies, to some extent, in nearly all cases of family predisposition, as when the son of a consumptive father is attacked with the disease, it is often difficult to say for a certainty that the son's disease is hereditary and has not been acquired, especially if, as may be the case, his brothers are quite exempt.

We must therefore take into consideration all degrees of family predisposition, and try to estimate each at its proper worth.

It may be remarked in passing, that man is not the only animal cursed with hereditary consumptive disease. Delafond states that a phthisical ram in a flock of merinoes transmitted his disease to sixteen or twenty of his progeny. Dr. Sanderson told me that at the great cattle breeding establishment at Lyons, the offspring of a Scotch bull whose lungs were found to be stuffed with tubercle, after his death, were also infected with the disease, and several of the guinea-pigs who were tuberculized in the late experiments have produced tuberculous offspring.

We must not overlook the fact, that it is not necessary for parents to have consumptive disease in order to produce phthisical offspring. The children of very aged parents, of syphilitic, gouty, or asthmatic' parents, or of those whose constitutions have been greatly weakened by drink, sexual indulgence, or other debilitating causes, are prone to phthisis. We cannot agree with Niemeyer, that

The tendency of asthmatic parents to produce phthisical children is hardly sufficiently recognised. Among my out-patients at Brompton I found many instances, and our tables include several cases.

The reason of this probably is, that many cases of asthma were at their commencement cases of limited phthisis, which have been arrested. In the course of this process induration at the root of the lung has taken place, causing contraction of the bronchi, and giving rise to asthmatic symptoms. (See p. 38.) The children of these patients, if phthisical at all, are generally more decidedly so than the parents.

these parents are as liable as consumptive parents to beget children who come into the world with a predisposition to consumption; on the contrary, the proclivity is present to a far less extent than those in whom family predisposition is strongly marked.

The extent in which hereditary predisposition exists among cases of phthisis, is a subject on which authorities differ; but these differences, as Dr. Fuller remarks, are attributable to the various degrees of relationship included. The 1,010 cases of the Brompton Hospital Report, included only parents, and gave an average of 24.4 per cent. Dr. Fuller's 385 cases embraced grand-parents, uncles and aunts, and furnished 59 per cent. Dr. Cotton's 1000 cases included parents, brothers and sisters, giving 36.7 per cent., and Dr. Pollock's 1,200 similarly estimated, showed 30 per cent.

Dr. Copland gives 47 per cent., but does not state his number of cases or the list of relations included. Louis, Briquet, and Rufz base their calculations on so small a number of patients, as hardly to furnish fair evidence, but, as far as it goes, it is confirmatory of the above estimates.

Our 1,000 cases give 484 instances, the particulars of which may here be seen:

cousins affected.

father's or mother's family affected (particulars unknown).
brothers and sisters affected.

484

Where more than one relation was affected, as was the case in 60 of these patients, it has been the rule not to make a double entry, but to record the nearest relative of

FAMILY PREDISPOSITION,

6

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the preceding generation: e.g., mother and brother' affected is entered under mother,' father and sister' under father,' and so on. 6 The greater number of duplicates occurred in those of the same generation as, brothers, sisters, and cousins.

1

Our percentage of family predisposition was 48.4, but, as will be seen by the above table, the number of purely hereditary cases, that is, with parents alone affected, was only 12 per cent., thus differing greatly from the percentages of 1 Drs. Cotton and 2 Fuller, and of the first Brompton Hospital Report, which was about 25. The only explanation we can offer of the discrepancy, is a difference in the class of the patients, from which our statistics are taken, and of those on which the above authorities found their estimate. Their calculations were based on hospital practice, (except Dr. Fuller's, which included some private patients): ours are based entirely on private practice.

Great pains were taken by Dr. Williams to arrive at an accurate result. The patients were all closely questioned as to their dead and living relations. In many

instances, the existence of consumption in the family was at first denied; but after cross-questioning, not only was its existence admitted, but undoubted cases of death from that disease were traced among their relatives.

On the whole, we think that an average of 12 per cent. for direct hereditary predisposition, and of 48 per cent. for family predisposition, are not unfair estimates for the upper classes, and that the average of the above authorties is probably correct for the lower classes; and we think it also likely that our smaller percentage in a class, which from its wealth is able to banish many of the most fertile causes of phthisis, gives a more just estimate of the influence that hereditary predisposition, unaided by poverty and exposure to divers pernicious influences, exercises on

the causation of phthisis. Having discussed the prevalence of family predisposition, we now proceed to consider the following questions regarding its transmission.

First, the influence of sex.

(1). Family predisposition is much more common among women than among men. This was clearly proved, as far as hereditary influence is concerned, by the first Brompton Hospital Report, which showed that, in this particular, the relative proportions of the sexes were as two to one. Our own cases of family predisposition show similar, though, as might be expected from the wider list of relations included, less striking evidence. Fifty-seven per cent. of the females, and only forty-three per cent. of the males, were thus affected. The more common occurrence of this feature among females than among males is to be accounted for on the ground that the sedentary and less invigorating life of the former offers less opposition to the development of the seeds of the malady; whereas the more vigorous and active life of a man tends to fortify a naturally delicate frame, and render the predisposition inert. Again, where the sons of phthisical fathers lead very sedentary lives, how very common it is for them to be attacked with consumption at an early age, and often of an acute description! This observation thus confirms what has been suggested with regard to the hereditary prevalence among females.

(2). The transmission of phthisis is more common through the mother than through the father. Mr. Ancell states that, as far as limited statistics go, the evidence on this point is strong. We are glad to be able· to confirm this statement, from our own statistics, which, in 1,000 cases, record sixty-seven consumptive mothers against forty-three consumptive fathers. Mr. Ancell justly remarks: Regarding it (phthisis) as a disease of 14 Treatise on Tuberculosis, p. 385.

PARENTAL TRANSMISSION.

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the blood, this result might have been predicated, since there is only one period at which the father's influence could be exercised, viz., that of conception; whereas the influence of the mother is exercised at that period, and also through uterine gestation.'

(3). Fathers transmit more frequently to sons, and mothers to daughters, than the converse. This important fact was first established by the first Brompton Hospital Reports, and having been amply confirmed by numerous competent observers, may now be said to be matter of every-day experience.

1

Our

How does family predisposition influence age in consumption? This is a very important question, bearing intimately on the prognosis of the disease, and deserves a fuller discussion than we have time or space for. researches have, we trust, cleared up some of the mystery in which the connection of age and family predisposition was enveloped. We have demonstrated clearly that the chief influence which family predisposition exercises is on the age at which the patient is likely to be attacked.

It hurries the onset of the disease. This conclusion was arrived at by careful investigation of the age at which the 1,000 private cases were attacked. This having been ascertained, we pursued a similar enquiry with regard to those affected with family predisposition; and lastly, with reference to those who were free from it, as far as could be ascertained at the time of their being under observation, that is to say, who up to the last date had had no relatives affected with phthisis. The result is shown on the next page:—

'On the Duration of Phthisis, and certain Conditions which Influence it,' Medico-Chir. Trans., vol. liv.