1883.] 



MICROSCOPICAL JOURNAL. 



55 



of body, it is not practicable, hence 

 the front surface of the front lens is 

 generally taken as the standard, and 

 the image is measured at a distance 

 of lo inches from this point. The 

 best way of doing this is by placing 

 a micrometer on the stage and a 

 piece of finely ground glass at the 

 end of the body instead of the eye- 

 piece. The distance of the ground 

 glass from the front of the objective 

 should be ten inches. If the mi- 

 crometer be now illuminated by very 

 intense lamp light, or in the case of 

 the higher powers by sunlight, and 

 carefully focussed, the image of the 

 lines will be seen on the ground 

 glass. Their distance apart may 

 then be dotted on the ground glass 

 and then carefully measured. It the 

 distance apart of the dots upon the 

 ground glass be now divided by the 

 real distance of the lines on the mi- 

 crometer, the linear amplification will 

 be the result. 



The power of the eye-piece may 

 now be determined from that of the 

 objective. The ey^-piece should be 

 placed in the tube, with its field-lens 

 in the case of a negative eye-piece 

 and its focal point in the case of a 

 positive eye-piece, at a distance of 

 ten inches from the front lens of the 

 objective. The power of the micro- 

 scope should now be taken at ten 

 inches with the camera-lucida in the 

 usual way. The power of the micro- 

 scope, divided by the previously de- 

 termmed power of the objective, will 

 give the power of the eye-piece in 

 diameters. 



The Cause of Tubercle.* 



I have been asked to say a few 

 words concerning the Bacillus hiber- 

 culosis. The subject has already 

 been so ably brought before us by 

 Dr. Schoney, that I shall not take up 

 much time this evening. First I wish 

 to briefly allude to the specimen of 



* Read Feb. i6th before the New York Mi- 

 croscopical Society. 



Bacillus on the slide to be shown by 

 Mr. Mead. I have examined it with 

 care, but I have failed to observe the 

 peculiar split or forked end which is 

 said by the original discoverer. Dr. 

 Koch, to be characteristic of the Ba- 

 cillus. I am inclined to doubt if the 

 ends of the Bacillus are really split. 

 On the slide of Mr. Mead I have seen 

 an appearance of cleft ends which 

 was purely an illusion caused by the 

 inclined position of so)ne of the Bacilli 

 with reference to the vertical axis of 

 the microscope. Slight changes of 

 the focus produce a false image of 

 the end of each rod, which appears 

 like a branch or fork running out froni 

 the true image. I regret not to have 

 the original article by Dr. Koch, to 

 assist in identifying the bacillus on 

 Mr. Mead's slide, but Dr. Schoney has 

 stated the length of the rods of 

 Koch's Bacillus to be YaooU of an inch. 

 These measure about ftVo^ of an inch, 

 and are, theiefore, very much longer 

 than Dr. Koch's species. 



The experiments of Dr. Koch to 

 prove that the Bacillus is the true 

 cause of tubercular disease have been 

 regarded as conclusive by many ob- 

 servers, but there is still a large num- 

 ber of physicians who doubt not only 

 the conclusive nature of the experi- 

 ments, but even the contagiousness of 

 the disease itself. 



Clinical experience affords much 

 opportunity for differences of opinion 

 concerning this subject. The impres- 

 sion that consumption is a contagious 

 disease was held by Galen, and since 

 his time it has always had more or 

 less support by the medical fraternity. 

 Yet it is universally conceded that not 

 all persons are readily affected by the 

 disease. Dr. Sternberg has made a 

 few experiments by inoculating ani- 

 mals with tubercular matter. Three 

 out of six experiments resulted in the 

 devolopment of tubercles and the 

 characteristic Bacillus. Dr. Janeway, 

 of this city, has given some valuable 

 information on this subject in an arti- 

 cle on the " Possible Contagion of 

 Phthisis," published xwxSxq Archives oj 



