222 



NA TURE 



\Ja7i. II, 1877 



of a historical or philological discussion, that such criticism 

 is a mere waste of time on the part of its author, and wholly 

 undeserving of attention on the part of those who are criti- 

 cised. Take it then as an illustration of the importance of 

 biological study, that thereby alone are men able to form 

 something like a rational conception of what constitutes 

 valuable criticism of the teachings of biologists.^ 



Next, I may mention another bearing of biological 

 knowledge — a more practical one in the ordinary sense of 

 the word. Consider the theory of infectious disease. 

 Surely that is of interest to all of us. Now the theory of 

 infectious disease is rapidly being elucidated by biological 

 study. It is possible to produce from among the lower 

 animals cases of devastating diseases which have all the 

 appearance of our infectious diseases, and which are cer- 

 tainly and unmistakably caused by living organisms. This 

 fact renders it possible, at any rate, that that doctrine of 

 the causation of infectious disease which is known under 

 the name of " the germ theory " may be well-founded ; 

 and if so it must needs lead to the most important prac- 

 tical measures in dealing with those most terrible visita- 

 tions. It may be well that the general as well as the 

 professional public should have a sufficient knowledge of 

 biological truths to be able to take a rational interest in 

 the discussion of such problems, and to see, what I think 

 they may hope to see, that, to those who possess a suffi- 

 cient elementary knowledge of Biology, they are not all 

 quite open questions. 



Let me mention another important practical illustration 

 of the value of biological study. Within the last forty years 

 the theory of agriculture has been revolutionised. The 

 researches of Liebig, and those of our own Lawes and 

 Gilbert, have had a bearing upon that branch of industry 

 the importance of which cannot be over-estimated ; but 

 the whole of these new views have grown out of the 

 better explanation of certain processes which go on in 

 plants, and which of course form a part of the subject- 

 matter of Biology. 



I might go on multiplying these examples, but I see 

 that the clock won't wait for me, and I must therefore 

 pass to the third question to which I referred : — Granted 

 that Biology is something worth studying, what is the best 

 way of studying it ? Here I must point out that, since Bio- 

 logy is a physical science, the method of studying it must 

 needs be analogous to that which is followed in the other 

 physical sciences. It has now long been recognised that if 

 a man wishes to be a chemist it is not only necessary that 

 he should read chemical books and attend chemical lec- 

 tures, but that he should actually for himself perform 

 the fundamental experiments in the laboratory, and know 

 exactly what the words which he finds in his books and 

 hears from his teachers, mean. If he does not do that he may 

 read till the crack of doom, but he will never know much 

 about chemistry. That is what every chemist will tell you, 

 and the physicist will do the same for his branch of 

 science. The great changes and improvements in physical 

 and chemical scientific education which have taken place 

 of late have all resulted from the combination of practical 

 teaching with the reading of books and with the hearing 

 of lectures. The same thing is true in Biology. Nobody 



' Some critics do not even take the trouble to read. I have recently been 

 adjured with much solemnity, to state publicly why I have " changed " my 

 opinion as to the value of the palEeontological evidence of the occurrence of 

 evolution. 



To this my reply i?, Why should I when that statement was made seven 

 years ago ? An address delivered from the Presidential Chair of the Geolo- 

 gical Society in 1870 may be said to be a public document, inasmuch as it 

 not only appeared m the yournal of that learned body, but was re-published 

 in 1873 in a volume of " Critiques and Addresses," to which my name is 

 attached. Therein will be found a pretty full .statement of my reasons for 

 enunciating two propositions : (il that " when we turn to the higher Verte- 

 hrata, the results of recent investigations, however we rhay sift and criticise 

 them, seem to me to leave a clear balance in favour of the evolution of living 

 forms one from another ; " and (2) that the case of the horse is one which 

 "will stand rigorous criticism." 



Tlius I do not see clearly in what way I can be said to have changed ray 

 opinion, except in the way of intensifying it, when in consequence of the 

 accumulation of similar evidence since 1870, I recently spoke of the denial of 

 evolution as not worth serious consideration. 



will ever know anything about Biology except in a dilet- 

 tante "paper-philosopher" way, who contents himself with 

 reading books on botany, zoology, and the like ; and the 

 reason of this is simple and easy to understand. It is that 

 all language is merely symbolical of the things of which 

 it treats ; the more complicated the things, the more 

 bare is the symbol, and the more its verbal definition 

 requires to be supplemented by the information derived 

 directly from the handling, and the seeing, and the touch- 

 ing of the thing symbolised: — that is really what is at the 

 bottom of the whole matter. It is plain common sense, as 

 all truth, in the long run is only common sense clarified. 

 If you want a man to be a tea merchant, you don't tell 

 him to read books about China or about tea, but you put 

 him into a tea-merchant's office where he has the handling, 

 the smelling, and the tasting of tea. Without the sort of 

 knowledge which can be gained only in this practical 

 way his exploits as a tea merchant will soon come to a 

 bankrupt termination. The " paper-philosophers " are 

 under the delusion that physical science can be mastered 

 as literary accomplishments are acquired, but unfor- 

 tunately it is not so. You may read any quantity of 

 books, and you may be almost as ignorant as you were 

 at starting, if you don't have, at the back of your minds, 

 the change for words in definite images which can only 

 be acquired through the operation of your observing 

 faculties on the phenomena of nature. 



It may be said : — " That is all very well, but you told 

 us just now that there are probably something like a 

 quarter of a million different kinds of living and extinct 

 animals and plants, and a human life could not suffice 

 for the examination of one-fiftieth part of all these." That 

 is true, but then comes the great convenience of the way 

 things are arranged ; which is, that although there are 

 these immense numbers of different kinds of living things 

 in existence, yet they are built up, after all, upon mar- 

 vellously few plans. 



There are, I suppose, about 100,000 species of insects, 

 if not more, and yet anybody who knows one insect — if a 

 properly chosen one — will be able to have a very fair con- 

 ception of the structure of the whole. I do not mean to 

 say he will know that structure thoroughly or as well as it 

 is desirable he should know it, but he will have enough 

 real knowledge to enable him to understand what he 

 reads, to have genuine images in his mind of those 

 structures which become so variously modified in all the 

 forms of insects he has not seen. In fact, there are such 

 things as types of form among animals and vegetables, 

 and for the purpose of getting a definite knowledge of 

 what constitutes the leading modifications of animal and 

 plant life it is not needful to examine more than a com- 

 paratively small number of animals and plants. 



Let me tell you what we do in the biological labora- 

 tory in the building adjacent to this. There I lecture to 

 a class of students daily for about four-and-a-half months, 

 and my class have, of course, their text-books ; but the 

 essential part of the whole teaching, and that which I 

 regard as really the most important part of it, is a labo- 

 ratory for practical work, which is simply a room with 

 all the materials arranged for ordinary dissection. We 

 have tables properly arranged in regard to light, micro- 

 scopes, and dissecting instruments, and we work through 

 the structure of a certain number of animals and 

 plants. As, for example, among the plants, we take a 

 yeast plant, a Fj-otococais, a common mould, a Chara, a 

 fern, and some flowering plant ; among animals we ex- 

 amine such things as an amasba, a vorticella, and a 

 fresh-water polype. We dissect a star-fish, an earth- 

 worm, a snail, a squid and a fresh- water mussel. We 

 examine a lobster and a cray-fish, and a black beetle. We 

 go on to a common skate, a cod-fish, a frog, a tortoise, a 

 pigeon, and a rabbit, and that takes us about all the time 

 we have to give. The purpose of this course is not to 

 make skilled dissectors, but to give every student a clear 



