October 6, 1898] 



NATURE 



ODD 



r 



substance and structure man and the lower animals are one." 

 Whatever opinion one may hold as to the origin of mankind, 

 the conviction as to the fundamental correspondence of human 

 organisation with that of animals is at present universally 

 accepted. 



Omnis Cellula e Cellula. 

 . . . The greatest difficulty in the advance of biology has 

 been the natural tendency of its disciples to set the search after 

 the unity of life in the forefront of their inquiries. Hence arose 

 the doctrine of vital force, an. assumption now discarded, but 

 still revealing its influence from time to time in isolated errors. 

 No satisfactory progress can be made till the idea of highly- 

 organised living things as units had been set aside ; till it was 

 recognised that they were in reality organisms, each constituent 

 part of which had its special life. Ultimate analysis of higher 

 animals and plants brings us alike to the cell, and it is these 

 single parts, the cells, which are to be regarded as the factors of 

 existence. The discovery of the development of complete 

 beings from the ova of animals and the germ-cells of plants has 

 bridged the gap between isolated living cells and complete 

 organisms, and has enabled the study of the former to be 

 employed in elucidating the life of the latter. In a medical 

 school where the teaching is almost exclusively concerned with 

 human beings this sentence should be writ large: — "The 

 organism is not an individual, but a social mechanism." Two 

 corollaries must also be stated — (i) that every living organism, 

 like every organ and tissue, contains cells ; (2) that the cells 

 are composed of organic chemical substances, which are not 

 themselves alive. The progress of truth in these matters 

 was much retarded by that portion of Schwann's cell-theory 

 which sought to establish the existence of free cell-formation, 

 which really implied the revival of the old doctrine of 

 spontaneous generation. This belief was gradually driven out 

 of the domain of zoology, but in connection with the formation 

 of plastic exudates found a sanctuary in thai of pathology. I 

 myself was taught the discontinuity of pathological growths — a 

 view which would logically lead back to the origin of living 

 from non-living matter. But enlightenment in this matter came 

 to me. At the end of my academical career I was acting as 

 clinical assistant in the eye department of the Berlin Hospital, 

 and I was struck by the fact that keratitis and corneal wounds 

 healed without the appearance of plastic exudation, and I was 

 thus led to study the process of inflammation in other non- 

 vascular structures, such as articular cartilages and the intima of 

 the larger vessels. In no one of these cases was plastic exuda- 

 tion found, but in all of them were changes in the tissue cells. 

 Turning next to vascular organs, and in particular those which 

 are the common seats of exudation processes, I succeeded in 

 demonstrating that the presence of cells in inflammatory exudates 

 was not the result of exudation, but of multiplication of pre- 

 existing cells. Extending this to the growth in thickness of the 

 long bones — which was ascribed by Duhamel to organisation of 

 a nutricious juice exuded by the periosteal vessels — I was thus 

 eventually able to extend the biological doctrine of omnis cellula 

 e cellula to pathological processes as well ; every new formation 

 presupposing a matrix or tissue from which its cells arise and 

 the stamp of which they bear- 



Heredity. 



Herein also lies the key to the mystery of heredity. The 

 humoral theory attributed this to the blood, and based the most 

 fantastic ideas upon this hypothesis; we know now that the cells 

 are the factors of the inherited properties, the sources of the 

 germs of new tissues and the motive power of vital action. It 

 must not, however, be supposed that all the problems of heredity 

 have thus been. solved. Thus, for instance, a general explanation 

 of theromorphism, or the appearance of variations recalling the 

 lower animals, is still to be found. Each case must be studied 

 on its merits, and an endeavour made to discover whether it 

 arose by atavism or by hereditary transmission of an acquired 

 condition. As to the occurrence of the latter mode of origin, 

 I can express myself positively. Equally difficult is the question 

 of hereditary diseases ; this is now generally assumed to depend 

 on the transmission of a predisposition which is present, though 

 not recognisable, in the earliest cells, being derived from the 

 paternal or maternal tissues. But the most elaborately con- 

 structed doctrines as to the hereditariness of a given disorder 

 may break down before the discovery of an actual causa viva. 

 A notable example of this is found in the case of leprosy, the 



NO. I 5 10, VOL. 58] 



transmission of which by inheritance was at one time so firmly 

 believed in that thirty years ago a law was nearly passed in 

 Norway forbidding the marriage of members of leprous families. 

 I myself, however, found that a certain number of cases at any 

 rate did not arise in this way, and my results were confirmed by 

 the discovery of the leprous bacillus by Armauer Hansen. In a 

 moment the hereditary theory of the disease was overthrown 

 and the old view of its acquirement by contagion restored. 

 Precisely the same happened a few decades earlier with 

 regard to favus and scabies. Another instructive condition is 

 that known as Heterotopia in which fragments of tissues or 

 organs are found dwelling in a situation other than that which 

 is normal to them. This is particularly the case with certain 

 glands, such as the thyroid and suprarenal, but is also known 

 with cartilage, teeth, and the various constituents of dermoids. 

 It no doubt occurs by process of transplantation, the misplaced 

 tissues developing no new properties, but merely preserving their 

 normal powers of growth. The attempt to generalise from this 

 fact and to attribute all tumour-formation to this cause carries 

 the idea beyond its proper scientific limits. 



Parasitism and Infection. 

 With regard to the subject of parasitism, the progress ot 

 scientific observation was retarded for centuries by the pre- 

 valence of the assumption made by Paracelsus that disease in 

 general was to be regarded as a parasite. Pushed to its logical 

 conclusion, this view would imply that each independent living 

 part of the organism would act as a parasite relatively to the 

 others. The true conception of a parasite implies its harmfulness 

 to its host. The larger animal parasites have been longest 

 known, but it is not so many years since their life-history has 

 been completely ascertained and the nature of their cysts 

 explained, while an alternation of generations has been dis- 

 covered in those which are apparently sexless. Very much 

 more recent is the detection of the parasitic protozoa, by which 

 the occurrence of the tropical fevers may be explained. As yet 

 we have not complete knowledge as to their life-history, but we 

 hold the end ot the chain by which this knowledge can be 

 attained. The elite of the infectious diseases are, however, the 

 work of the minutest kind of parasitic plants, bacteria, the 

 scientific study of which may be said to date from Pasteur's 

 immortal researches upon putrefaction and fermentation. The 

 observation of microbes under exact experimental conditions, 

 and the chemical investigation of their products opened up the 

 modern field of bacteriology, a science among the early triumphs 

 of which were the discoveries of the bacilli of tubercle and 

 Asiatic cholera by Robert Koch. In connection with this 

 subject, three important landmarks require comment. One is 

 the necessity for distinguishing between the cause and the 

 essential nature of infectious diseases, the latter of which is 

 determined by the reaction of the tissues and organs to microbes. 

 Secondly, there is the relation between the smaller parasites and 

 the diseases determined by them. This may be summed up in 

 the general word (introduced by Prof. Virchow himself) " infec- 

 tion." But to assume that all infections result from the action 

 of bacteria is to go beyond the domain of present knowledge, 

 and probably to retard further progress. The third point is the 

 question as to the mode of action of infection. It is only the 

 larger parasites whose main effect is the devouring of parts of 

 their hosts ; the smaller act mainly by the secretion of virulent 

 poisons. The recognition of this latter fact has led to the 

 brilliant work of Lister on the one hand, and to the introduction 

 of serum-therapeutics on the other. 



Antiseptic Surgery. 

 It would be carrying coals to Newcastle were I to sketch in 

 London the beneficial effects which the application of methods 

 of cleanliness has exercised upon surgical practice. In the city 

 wherein the man .still lives and works who, by devising this 

 treatment, has introduced the greatest and most beneficent 

 reform that the practical branches of medical science have ever 

 known, every one is aware that Lord Lister, on the strength of 

 his original reasoning, arrived at practical results which the new 

 theory of fermentative and septic processes fully confirmed. 

 Before any one had succeeded in demonstrating by exact 

 methods the microbes which are active in different diseases, 

 Lister had learnt, in a truly prophetic revelation, the means by 

 which protection against the action of putrefactive organisms 

 can be attained. The opening up of further regions of clinical 

 medicine to the knife of the surgeon and a perfect revolution in 



