TRANSACTIONS OF THE SECTIONS. 81 



The contents of each of these vesicles is 0-000,000,523,599 cubic inches. 

 Superficies ... ... is 0'000,314,181 square inches. 



The aggregate superficies of the whole is 60,000 square inches. 

 The increase of superficies arising from the additional quantity of one cubic inch 

 equally distributed through the whole, is 40-347 square inches, equal to 2-8 square feet. 



That arising from 5 cubic inches is . 1987 13-79 



20 ... . 7621 52-9 



The correctness of these views was also inferred from stethoscopic phenomena in 

 health and disease. 



On a general Law of vital Periodicity. By Thomas Laycock, M.D., 

 M.R.C.P., London, F.R.M.C.S., Physician to the York Dispensary. 



The object of this paper is to establish, by induction, a law of periodicity, with a 

 term of seven days, pervading the entire animal kingdom, and influencing the mani- 

 festations of disease in man. The facts brought forward for this purpose are derived 

 from periods of gestation, or of hatching, in fishes, reptiles, birds, and mammals ; 

 from the transformations and habits of insects ; from the effects of morbid poisons on 

 the animal economy, as more particularly exhibited in malarious, exanthematous, and 

 infectious fevers ; and from the phsenomena of gout and the mutations of chronic 

 diseases. In all of these classes of facts a periodical movement is found, with a strict 

 reference to seven days, or its submultiple or multiple. Of the numerous facts stated 

 the following are examples : of 129 species of birds and mammals, whose period of 

 utero-gestation or incubation was examined, in 67 the period was a definite number of 

 weeks or months. 24 were within one day of being so, and in the remaining 39 the 

 period was so loosely stated as not to be of much weight for or against the accuracy 

 of the measure of time adopted by the author. As special examples, it is stated that 

 the period of incubation in the Grallidse, Tetraonidse, and other birds of about the 

 same size, is three weeks ; in the Anatidse four weeks ; the Cygnidse six weeks ; 

 but in small birds, as the Museiparse, only two weeks. The period of hatching in the 

 salmon is exactly twenty weeks; in the wasp, common bee, and ichneumon, half a 

 week, or seven lunar days; in other insects a week and a half, as in the Tenthredo 

 capr&a, or gooseberry gnat ; while in the mole-cricket it is four weeks, and in the 

 glow-worm six weeks. The author states, that the most remarkable confirmations of 

 the law are to be found in insects by observing the periods regulating — first, the de- 

 velopment of the ovum ; second, the duration of the larva state, and the moults which 

 take place in this stage of development; third, the duration of the pupa, or chrysalis 

 period ; and fourth, of the imago state, or puberty, and of the vital manifestations 

 then developed. Numerous examples from these conditions in many species are 

 given, in all which a period of seven days, or its simple multiple, is traced. The 

 phsenomena of disease in man are next examined in the order previously mentioned ; 

 and the author endeavours to show that the stages, the duration, and the principal 

 changes of the whole class of febrile diseases, are governed by the same law, which 

 really afforded the grounds for the establishment of the critical days of Hippocrates ; 

 of these days, the most important being the seventh, fourteenth, and twenty-first, and 

 the next in importance the fourth, seventh, and eleventh, the half-periods. The law- 

 is next traced through a paroxysm of gout, and through chronic diseases; and it is 

 observed that the doctrine of " septenaries," which prevailed among the ancient phy- 

 sicians, was founded on similar observations, by whom the fact of vital periodicity was 

 assumed, as if it were too well known to be doubted. 



By extending this law to health and the performance of healthy functions, the 

 author shows how it explains some hitherto inexplicable facts in pathology ; as, for 

 example, the latent periods of fever, and the limitation of them to a period of twenty- 

 eight days. The extension of an epidemic amongst an entire population is also regu- 

 lated by it; and, according to the author's views, the individuals of a single family, 

 that is, of those born of a common mother, will be attacked at intervals of time regu- 

 lated by the measure he has developed in the general law. It is remarked that those 

 fevers, "one attack of which affords immunity from a second, exhibit invariably the 

 quartan type ; or, in other words, are measured by the half-period ; and that this 

 general fact must be considered of some importance in discussing the vexed question 

 of contagion. The inquiry into the efficacy of remedial agencies may be rendered 



1842. G 



