16 



THE AMERICAN MONTHLY 



[January, 



a valuable review is given of the whole 

 subject of bacteria and their relation 

 to diseases; but we cannot now no- 

 tice them more fully, and the reports 

 of Drs. Law, Detmers, and others, 

 must be "passed over with only this 

 reference. There is also printed a 

 translation of some articles by M. 

 Pasteur, and by others, read before the 

 French Academy of Sciences concern- 

 ing the etiology of charbon. 



The importance of these investiga- 

 tions, conducted by the Department 

 of Agriculture, is not readily overes- 

 timated, and the liberality with which 

 the illustration and publication of the 

 reports is provided for, indicates that 

 the value of the thorough scientific 

 study of such diseases, to the agricul- 

 tural and commercial interests of the 

 country, is fully recognized by the 

 Department. These investigations 

 require not only the best instruments 

 for observation, but also a thorough 

 knowledge of the subject on the part 

 of the investigators, combined with 

 skill and experience as observers. 

 The reports of the Department already 

 show that the truly scientific method 

 has not been followed by every inves- 

 tigator who has been entrusted with 

 the microscopical study of the schizo- 

 phytes of disease. Hasty and erro- 

 neous conclusions have been reached, 

 where a more profound knowledge of 

 the work of others would have been 

 a safeguard against them. But on the 

 whole, the work has been well done, 

 and we trust it will be continued in a 

 manner as satisfactory as it has been 

 in the past. 



o 



Large and Small Microscopes. 

 — Mr. Stodder is so persistent in his 

 arguments on this subject, that we 

 deem it worth while to present the 

 opposite side more fully than hereto- 

 fore, indicating the reasons for the 

 position we have taken. We have 

 supposed our readers would see clear- 

 ly enough, why a small stand, if it 

 can be made to do the work of a 

 large one equally well, is more con- 

 venient than the latter, and we have 



not, nor do we now, deem it worth 

 while to spend any time in the dis- 

 cussion of that question. But Mr. 

 Stodder denies even this. We will 

 not attempt to demonstrate that he 

 is in error, but willingly leave the de- 

 cision of a mere matter of opinion 

 like this to the judgment of our 

 readers. 



Mr. Stodder seems to think small 

 stands are necessarily made with 

 short tubes of small diameter, and 

 that they cannot be used for all pur- 

 poses. But in this, he is quite wrong. 

 By a small stand we mean one about 

 the size of Mr. Bulloch's " Biological," 

 and, as for the size of the tube, we 

 would have it of the standard which 

 may be recommended by the Ameri- 

 can Society of Microscopists, what- 

 ever that proves to be. The length 

 of the tube is a matter of compara- 

 tively little importance. It may be 

 ten inches or it may be less. We 

 think it should be ten inches with 

 the draw-tube out, merely because 

 English and American objectives are 

 corrected for tubes of that length. 

 Lest there should be any misappre- 

 hension about the advantage of a 

 large over a small tube, it may be said 

 that for each focus of ocular, there is 

 a certain limit for the diameter of 

 the tube, beyond which there is no 

 advantage in further enlargement. 

 If we established a definite focus for 

 an "A " ocular, then the best size for 

 the tube will be just large enough to 

 utilize the full aperture of the field- 

 lens of that ocular. Practically, there 

 is a limit to the diameter of the field- 

 lens. Hence a tube exceeding that 

 limit affords no advantages. But as 

 the higher oculars are used, the 

 available diameters of the field-lenses 

 become smaller. Hence, a "B " ocu- 

 lar does not require, for perfect ac- 

 tion, so large a tube as the " A ;" the 

 "C," does not require one so large as 

 the "B," etc. It is probable, there- 

 fore, that the standard size of tube, if 

 ever adopted, will be determined by 

 the "A " ocular. 



We are now in a position to under- 



