152 BACTERIA IN RELATION TO PLANT DISEASES. 



the improvement of various kinds of apparatus, notably the microscope, and it has 

 derived corresponding advantages from the use of these improved instruments of 

 research. We owe, in particular, a great debt to the German physicist Abbe, whose 

 discovery of the Jena glass made possible the superb modern apochromatic objective. 



Among the multitude of workers in animal pathology and bacteriology during 

 the last thirty-five years certain men tower far above the rest, their contributions to 

 science having been more conspicuous and their imprint on their generation more 

 lasting. If France is mentioned, we think at once of Pasteur, Davaine, Duclaux, 

 Metchnikoff, Chamberlaud, Roux, Nocard, and Chauveau. In Germany we think 

 of Virchow, Cohn, Cohnheim, Koch, Weigert, Nicolaier, Eberth, Gaffky, Hueppe, 

 Fliigge, Fraenkel, Pfeiffer, Behring, Ehrlich, and many others ; in Japan, of Kitasato 

 and Shiga; in the United States, of Welch, Sternberg, Theobald Smith, Nuttall, 

 Councilman, and a host of brilliant younger men, many of whom received their 

 training under Welch in the Johns Hopkins Pathological Laboratory. England, 

 from which one might have expected so much, has contributed comparatively little, 

 owing probably to the laws in force in that country respecting animal experimenta- 

 tion, laws framed with the intention of doing a kindness to the lower animals, but 

 working, on account of their interference with the pathologist, a distinct detriment 

 both to men and animals, the aim of all animal pathological inquiry being the alle- 

 viation of human and animal suffering. In passing we should not forget, however, 

 the contributions of Tyndall and Lister, the one a physicist, the other a surgeon. 



Undoubtedly bacteriology owes very much to Louis Pasteur. France has had 

 many great sons, none greater than he. His refutation of the doctrine of spontane- 

 ous generation cleared the air of many misconceptions and laid the foundations for 

 exact experimentation. His demonstration of the nature of pebrine and flacherie, 

 two destructive diseases of silk worms, brought again into vivid light the assump- 

 tion that the origin of a great variety of human and animal diseases should be 

 sought in the activities of microscopic organisms. His studies of anthrax and 

 other diseases of warm-blooded animals confirmed this suspicion and set a great 

 many persons thinking and working. His investigations of the problems connected 

 with fermentation were similarly fertile in discovery and in suggestion. 



The publication of Robert Koch's great paper on tuberculosis in 1884 marked 

 another distinct advance. The same memorable year Koch published in full his 

 discovery of the cause of Asiatic cholera, only a brief announcement of it having 

 been made in 1883. The whole world was interested, and from this time on experi- 

 menters began to multiply in every civilized land, boards of health, universities, and 

 private citizens vying with each other in the establishment of laboratories for the 

 study of these minute organisms endowed with so much power for good or evil. 

 Koch's investigations in South Africa bring us down to recent times, where the per- 

 spective is not so good. To sum up very briefly, omitting many things, the following 

 are some of the milestones : 



1. Overthrow of the doctrine of spontaneous generation. 



2. Discovery that putrescible fluids (exclusive of milk) will not decay after 

 boiling, if protected from the bacteria of the air by means of cotton-plugs. 



