128 



THE AMERICAN MONTHLY 



[July, 



in this respect differing from an- 

 thrax bacilli, and Koch infers from 

 that that tuberculosis cannot arise 

 from the air, or from the water, or 

 from plants, but from animals, be- 

 cause the tuberculous bacilli can 

 only live at the temperature of ani- 

 mal life. 



By these experiments, laboriously 

 carried out with untiring patience, it 

 is proved in the most exact manner 

 that the bacilli brought to light first 

 by Koch, by the method of double- 

 staining of the tissues, are actually 

 the true pathogenic organisms of tu- 

 berculosis. 



I may be allowed here to digress 

 with a brief remark upon the impor- 

 tance of staining, which, by some mi- 

 croscopists has hitherto been under- 

 rated. Even a noted teacher of 

 histology recently took occasion to 

 ridicule this show of staining, which 

 he designates as an aesthetic luxury, 

 only good for public exhibition to 

 laymen, which, however, masks 

 more than represents the true na- 

 ture of tissues. Yet the use of 

 staining fluids is as important to 

 the scientific microscopist, and es- 

 pecially to the histologist, as the 

 spectroscope is to the chemist. It 

 enlarges his field, and brings out 

 to view distinctions, and differen- 

 tiates individuals of germs of a dis- 

 tinct protoplasmic nature and energy 

 akin to a certain reagent and not to 

 another, as the discovery of Koch 

 clearly shows. 



The great importance of the inves- 

 tigation of the etiology of infectious 

 diseases is apparent to everybody; to 

 the practitioner it opens the view, 

 though in the distant perspective, of 

 a possibility that a disease which, for 

 thousands of years has more than 

 decimated the human race, can be 

 caught and perhaps fought, literally 

 in its germs. 



Prof. Tyndall, in speaking of Dr. 

 Koch's discovery, in his enthusiasm 

 goes so far as to hint the suggestion 

 that these bacilli could probably be 

 modified by cultivation to a state in 



which they become prophylactic — as 

 vaccination in small-pox. Indeed, he 

 regards Koch's discovery as one of the 

 greatest events in science. I myself 

 think the truth or fallacy of this theo- 

 ry cannot be settled yet, and that it 

 requires further extended experi- 

 ments, especially on man himself — 

 perhaps on criminals, if their terms be 

 extended. For there are many ques- 

 tions to be raised against the con- 

 tagiousness of tuberculosis; for in- 

 stance why students who dissect 

 many such cadavers are not more 

 frequently infected by the poison, 

 and why widows or widowers of 

 a husband or wife dead of con- 

 sumption, do not as a rule, follow 

 them soon, out of tubercular sympa- 

 thy. These questions are not cleared 

 up yet, much less answered, nor are 

 the postulates of the epidemiological 

 experience done away with; but so 

 much is certain, that these admirable 

 experiments show the path by which 

 the certainty of decision can be reach- 

 ed. It is the duty of the microsco- 

 pists, the detectives in the corps of sci- 

 entists, to bring to light these invisi- 

 ble enemies to human life, to espy 

 and to find them; and the duty of 

 the physician to defy and fight them. 



Abstract of the Address of the 

 President of the Royal Micro- 

 scopical Society^ London, 



{Continued.) 



Mounting-media of High Re- 

 fractive Indices. — To utilize the 

 full benefit of immersion objectives, 

 it is of course essential that the ob- 

 ject should be mounted in a medium, 

 the refractive index of which is not 

 less than that of the immersion fluid; 

 and down to a comparatively recent 

 period Canada balsam was most com- 

 monly used for this purpose, particu- 

 larly for diatoms. 



Mr. Stephenson, however, pointed 

 out that although by the use of the 

 balsam we have attained our object 



