480 



NATURE 



{Sept. 13, 1888 



of certain kinds of disease can hardly be exaggerated. I have 

 already mentioned Henle as having first found the true clue to 

 animal histology in the structure of plants. As early as 1840 

 the same observer indicated the grounds for regarding con- 

 tagious diseases as due to living organisms. I will state his 

 argument in the words ofDe Bary, whose "Lectures on Bacteria," 

 the last work which we owe to his gifted hand, I can confidently 

 recommend to you as a luminous but critical discussion of a vast 

 mass of difficult and conflicting literature. 



It was, of course, clear that contagion must be due to the com- 

 munication of infectious particles or contagia. These contagia, 

 although at the time no one had seen them, Henle pointed out, 

 "" have the power, possessed, as far as we know, by living 

 creatures only, of growing under favourable conditions, and of 

 multiplying at the expense of some other substance than their 

 own, and therefore of assimilating that substance." Henle en- 

 forced his view by comparison with the theory of fermentation, 

 which had then been promulgated by Schwann. But for many 

 years his views found no favour. Botanists, however, as in so 

 many other cases, struck on the right path, and from about the 

 year 1850 steady progress, in which De Bary himself took a 

 leading part, was made in showing that most of the diseases of 

 plants are due to parasitic infection. The reason of this success 

 ■was obvious : the structure of plants makes them more accessible 

 to research, and the invading parasites are larger than animal 

 •contagia. On the animal side all real progress dates from about 

 i860, when Pasteur, having established Schwann's theory of 

 fermentation on an impregnable basis, took up Henle's theory 

 of living contagia. 



The only risk now is that we may get on too fast. To put 

 the true theory of any one contagious disease on as firm, a basis 

 as that of alcoholic fermentation is no easy matter to accomplish. 

 But I believe that this is, notwithstanding a flood of facile 

 speculation and imperfect research, slowly being done. 



There are two tracts in the body which are obviously accessible 

 to such minute organisms as Bacteria, and favourable for their 

 •development. These are the alimentary canal and the blood. 

 In the case of the former there is evidence that every one of us 

 possesses quite a little flora of varied forms and species. They 

 seem for the most part, in health, to be comparatively innocuous ; 

 •indeed, it is believed that they are ancillary to and aid digestion. 

 But it is easy to see that other kinds may be introduced, or those 

 already present may be called into abnormal activity, and 

 fermentative processes may be set up of a very inconvenient 

 kind. These may result in mere digestive disorder, or in the pro- 

 duction of some of those poisonous derivatives of proteids of 

 which I have spoken, the effect of which upon the organism 

 may be most disastrous. 



The access of Bacteria to the blood is a far more serious 

 •matter. They produce phenomena the obvious analogy of which 

 to fermentative processes has led to the resulting diseases being 

 called zymotic. Take, for example, the disease known as 

 ■" relapsing fever." This is contagious. After a period of 

 incubation, violent fever sets in, which lasts for something less 

 than a week, is then followed by a period of absence, to be again 

 followed in succession by one or more similar attacks, which 

 -ultimately cease. Now you will observe that the analogy to a 

 fermentative process is very close. The period of incubation is 

 the necessary interval between the introduction of the germ and 

 its vegetative multiplication in sufficient numbers to appreciably 

 affect the total volume of the blood. The rise in temperature 

 and the limited duration of the attack are equally, as we have 

 seen, characteristic of fermentative processes, while the bodily 

 exhaustion which always follows fever is the obvious result of the 

 dissipation by the ferment organisms of nutritive matter destined 

 for the repair of tissue waste. During the presence of this fever 

 there is present in the blood an organism, Spirochete obermeieri, 

 so named after its discoverer. This disappears when the fever 

 subsides. It is found that if other individuals are inoculated 

 with blood taken from patients during the fever attack, the 

 disease is communicated, but that this is not the case if the 

 inoculation is made during the period of freedom. The evidence, 

 then, seems clear that this disease is due to a definite organism. 

 The interesting point, however, arises, why does the fever recur, 

 and why eventually cease ? The analogy of fermentation leads 

 to the hypothesis that, as in the case of yeast, tne products of its 

 action inhibit after a time the further activity of the Spirochete. 

 The inhibiting substance is, no doubt, eventually removed par- 

 tially from the blood by its normal processes of depuration, 

 and the surviving indiv duals of Spirochete can then continue 



their activity, as in lactic fermentation. With regard to the final 

 cessation of the disease, there are facts which may lead one to 

 suppose that in this as in other cases sufficient of the inhibiting 

 substance ultimately remains in the organism to protect it 

 against any further outbreak of activity on the part of the 

 Spirochete. 



Here we have an example of a disease which, though having 

 a well-marked zymotic character, is comparatively harmless. In 

 anthrax, which is known to be due to Bacillus anthracis, we have 

 one which is, on the contrary, extremely fatal. I need not enter 

 into the details. It is sufficient to say that there is reason to 

 believe that the Bacillus produces, as one of those by-products of 

 protoplasmic destruction to which I have already alluded, a 

 most virulent poison. But the remarkable thing is that this 

 Bacillus, which can be cultivated externally to the body, if kept 

 at a heightened temperature, can be attenuated in its virulence. 

 It drops, in fact, the excretion of the poison. It is then found 

 that, if injected into the blood, it does no mischief, and, what is 

 more extraordinary, if the Bacillus in its most lethal form is 

 subsequently introduced, it too has lost its power. The explana- 

 tion of the immunity in this case is entirely different from that 

 which was suggested by a consideration of the facts of relapsing 

 fever. The researches of Metschnikoff have led to the hypothesis 

 that in the present case the white blood-corpuscles destroy the 

 Bacillus. When they first come into contact with these in their 

 virulent form, they are unable to tbuch them. But if they have 

 been educated by first having presented to them the attenuated 

 form, they find no difficulty in grappling with the malignant. 

 This is a very remarkable view. I should not have put it before 

 you had there not been solid reasons for regarding the idea 

 of the education of protoplasm with scientific respect. The 

 Plasmodia of the Myxomycetes, which consist of naked proto- 

 plasm, are known to become habituated to food which they at 

 first reject, and the researches of Beyerinck on the disease known 

 as "gumming" in plants have apparently shown that healthy 

 cells may be taught, as it were, to produce a ferment which 

 otherwise they would not excrete. 



If Metschnikoff's theory be true, we have a rational explana- 

 tion of vaccination and of preventive inoculation generally. It 

 is probably, however, not the only explanation. And the theory 

 of the inhibitive action upon itself of the products of the ferment- 

 organism's own activity is still being made the basis of experi- 

 ment. In fact, the most recent results point to the possibility 

 of obtaining protection by injecting into the blood substances 

 artificially obtained entirely independent of the organisms whose 

 development they inhibit. 



It is impossible for me to touch on these important matters at 

 any greater length, but I doubt if the theory of fermentation, as 

 applied to the diseases of organisms, has as yet more than 

 opened its first page. It seems to me possible that, besides the 

 rational explanation of zymotic diseases, it may throw light on 

 others where, owing to abnormal conditions, the organism, 

 as in the case of Berard's plums, is itself the agent in its own 

 fermentative processes. 



And now I must conclude. I have led you, I am afraid, a 

 too lengthy and varied a journey in the field of botanical study. 

 But to sum up my argument. I believe I have shown you that 

 at the bottom of every great branch of biological inquiry it has 

 never been possible to neglect the study of plants ; nay, more, 

 that the study of plant-life has generally given the key to the true 

 course of investigation. Whether you take the problems of 

 geographical distribution, the most obscure points in the theory 

 of organic evolution, or the innermost secrets of vital phenomena, 

 whether in health or disease, not to consider plants is still, in the 

 words of Mr. Darwin, " a gigantic oversight, for these would 

 simplify the problem." 



SECTION E. 



GEOGRAPHY. 



Opening Address by Colonel Sir C. W. Wilson, R-E. 

 K.C.B., K.C.M.G., D.C.L., LL.D., F.R.S., F.R.G.S., 

 Director-General of the Ordnance Survey, Presi- 

 dent of the Section. 



On opening the present session of the Geographical Section 

 of the British Association I cannot refrain from alluding to the 

 last occasion, now nearly a quarter of a century ago, upon which 

 it met in this city. The chair was then filled by one to whom I, 

 in common with others of the younger generation of that day, 



