C. U C. p. ALUMNI JOURNAL 



49 



out and examined directly or are sub- 

 jected to maceration and the pulp 

 examined. 



Bacteriological and Pathological Uses. 



The advances made in the sciences of 

 bacteriology and histologic pathology are 

 to a great extent due to increased 

 efficiency in the manufacture of higher 

 powered objectives. While not all the 

 work in these sciences requires the use 

 of the microscope, we find that the 

 greater portion of it does. Examination 

 of bacteriological and pathological speci- 

 mens demands the use of staining agents 

 and a small but important branch of 

 science has been brought into existence 

 through the study of these reagents, their 

 effects upon organisms and the reactions 

 involved. In examining most materials 

 included under this head we employ the 

 so-called oil immersion lenses. We find 

 that the higher powered objectives tend 

 to disperse light rays and that a thin 

 layer of air between the objective and 

 the specimen will have a refractive power 

 differing from that of* the glass in the 

 lenses of the objective. These factors 

 while not as noticeable in lower powered 

 objectives become very apparent in those 

 of higher magnification. The use be- 

 tween the lens and the object, of a 

 thickened oil of cedar-wood having a 

 refractive index near that of optical 

 glass, does away with these interfering 

 differences of refraction. It displaces 

 the air ordinarily occupying the space 

 between the objective and the specimen. 

 Microscopic examination is to a great 

 extent the means of positive diagnosis 

 in diseases such as tuberculosis, typhoid, 

 carcinoma, diphtheria, tetanus and many 

 others. 



Microchemical Methods. 



The use of the microscope in chemical 

 analysis is a branch which has as }et 

 hardly been worked. The great dif- 

 ficulties are inability to obtain exact 

 quantitative results and the lack of 

 workers who are well enough versed in 

 microchemical technic to have confidence 

 in their observations. The personal fac- 

 tor plays a larger part in microchemical 

 analysis than in the usual methods of 

 chemical analysis and much greater ex- 

 perience is required. These difficulties 

 tend to decrease the number of micro- 

 analysts who are capable of applying the 

 methods offered for the conduct of such 

 work. As we are dealing with very 

 small quantities of material we are also 

 increasing chances of error through 

 faulty manipulation. But if one has to 

 examine minute quantities of material, 

 especially the alkaloids and their salts, 

 microchemical methods prove a great 

 help. Microchemical analysis demands 

 a good working knowledge of crystal- 

 lography as we can often determine a 

 sample from its crystal formation. The 

 most useful accessory in this line of 

 work is the polarizing ocular. In modern 

 instruments this apparatus is readily 

 adjusted by the analyser section being 

 placed in the condenser mount and the 

 polarizer in the body-tube in place of the 

 usual ocular. 



Crystallized salts of the alkaloids are 

 a class of substances in which micro- 

 analytic methods of determination are as 

 certain, if not more so, then the usual 

 color tests employed. These color tests 

 are often indefinite and subject to many 

 interfering factors. They are in some 

 cases wholly empirical, the reactions con- 

 cerned in the production of the colors 



