A HALF-CENTURY OF SCIENCE. 73 



duction in the lower plants was doubtful, or at least doubted by some 

 eminent authorities, as recently as 1853, when the actual process of 

 fertilization in the common bladderwrack of our shores was observed 

 by Thuret, while the reproduction of the larger fungi was first worked 

 out by De Bary in 1863. 



As regards lichens, Schwendener proposed, in 1869, the startling 

 theory, now, however, accepted by some of the highest authorities, 

 that lichens are not autonomous organisms, but commensal associations 

 of a fungus parasitic on an alga. With reference to the higher cryp- 

 togams it is hardly too much to say that the whole of our exact knowl- 

 edge of their life-history has been obtained during the last half -cen- 

 tury. Thus, in the case of ferns, the male organs, or antheridia, were 

 first discovered by Nageli in 1844, and the archegonia, or female or- 

 gans, by Suminski in 1848. The early stages in the development of 

 mosses were worked out by Valentine in 1833. Lastly, the principle 

 of alternation of generations in plants was discovered by Hofmeister. 

 This eminent naturalist also, in 1851-54, pointed out the homologies 

 of the reproductive processes in mosses, vascular cryptogams, gymno- 

 sperms, and angiosperms. 



Nothing could have appeared less likely than that researches into 

 the theory of spontaneous generation should have led to practical im- 

 provements in medical science. Yet such has been the case. Only 

 a few years ago bacteria seemed mere scientific curiosities. It had 

 long been known that an infusion say, of hay would, if exposed to 

 the atmosphere, be found, after a certain time, to teem with living 

 forms. Even those few who still believe that life would be spontane- 

 ously generated in such an infusion, will admit that these minute or- 

 ganisms are, if not entirely, yet mainly, derived from germs floating 

 in our atmosphere ; and, if precautions are taken to exclude such 

 germs, as in the careful experiments especially of Pasteur, Tyndall, 

 and Roberts, every one will grant that in ninety-nine cases out of a 

 hundred no such development of life will take place. These facts 

 have led to most important results in surgery. One reason why com- 

 pound fractures are so dangerous, is because, the skin being broken, 

 the air obtains access to the wound, bringing with it innumerable 

 germs, which too often set up putrefying action. Lister first made a 

 practical application of these obseiwations. He set himself to find 

 some substance capable of killing the germs, without being itself too 

 potent a caustic, and he found that dilute carbolic acid fulfilled these 

 conditions. This discovery has enabled many operations to be per- 

 formed which would previously have been almost hopeless. 



The same idea seems destined to prove as useful in medicine as in 

 surgery. There is great reason to suppose that many diseases, espe- 

 cially those of a zymotic character, have their origin in the germs of 

 special organisms. We know that fevers run a certain definite course. 

 The parasitic organisms are at first few, but gradually multiply at the 



