Journal of Applied Microscopy. 



ened by using twenty cubic centimeters 

 of Valentine's meat juice instead of 

 making- the meat infusion as above indi- 

 cated. I specify "Valentine's, as it makes 

 a meat infusion of lighter color than any 

 other meat extract that I have tried, and 

 consequently a clearer and lighter col- 

 ored agar, equal in this respect, indeed, 

 to the agar made in the regular way. 

 W. W. Alleger. 

 Howard University, Washington, D. 

 C, Dec. 6, 1897. 



Class Technique in Pathology. 



Ernest B. Sangree, A. M., M. D., 



Professor of Pathology and Bacteriology in the 

 Medical Department of Vanderbilt Uni- 

 versity, Nashville, Tenn. 



Since much of the workl in a pathologi- 

 cal laboratory is essentially mechanical, 

 it is important in order to get the full 

 benefit of the laboratory period, that the 

 mechanical portion should be executed 

 in as speedy and systematic a manner 

 as possible. In the rather limited time 

 usually allotted to this subject, it does 

 not seem possible to have the students 

 do much of the section cutting them- 

 selves. They are so very unequal in me- 

 chanical ability, the majority poor, that 

 the results are likely to be bad. Good 

 mounts require thin sections, and it is, 

 therefore, my custom to have the blocks 

 of tissue hardened, embedded and cut by 

 my assistants. Celloidin is preferred for 

 class work, for in this way I can have 

 three or four hundred sections cut 

 months before hand and allowed to stand 

 away in bottles against the proper time. 

 Our sections are usually cut about twen- 

 ty micromillimeters thick, and on ac- 

 count of the enveloping celloidin matrix, 

 these sections can be handled by the 

 students as easily as naked sections 

 three times as thick. 



Before the hour, the sections for the 

 day are put in wide, flat dishes of wa.ter 

 in the laboratory, and each student 

 takes a section in a watch glass of water 

 to his desk. I think that double stain- 

 ing by logwood and eosin is by far the 

 most satisfactory routine method for 

 class work. For clearing I prefer creo- 

 sote. It must be the best beechwood. 

 This seems to take up more water in less 

 time than any other medium. Neither 

 does it dissolve the celloidin matrix nor 

 extract the eosin. But the most import- 

 ant part of laboratory teaching is 

 the demonstration. Evei-ything else is 

 subsidiary to that. Of what use is a 

 beautifully mounted specimen unless the 

 student understands it? Students at the 

 microscope require individual attention, 

 yet when there are forty or more in a 

 class, it becomes physically impossible 



to spend much time with each one. What 

 answers the purpose nearly as well, how- 

 ever, is the microscopic projection appa- 

 ratus. We have such an attachment to 

 our electrical lantern. At the beginning 

 of each lesson, the sections for the day, 

 previously stained, are thrown on the 

 screen by means of the 3-4 and 1-4 pro- 

 jection objectives. These objectives give 

 images sufficiently clear and well-deflned 

 so that everyone in a large room may 

 see. Since the section appears on the 

 screen exactly as it will under the in- 

 dividual microscope, ten or fifteen min- 

 utes spent in this way in pointing out the 

 elements of the specimen are almost 

 equal to the same time spent on each in- 

 strument. Further to facilitate actual 

 microscopic demonstration, I have had 

 placed half way across the eyepiece 

 diaphragm of each microscope a human 

 hair to act as a pointer. As this is in 

 focus along with the specimen, any ob- 

 ject which it is desired to point out to 

 the student can instantly be brought to 

 the end of the pointer by moving the 

 slide, and he cannot fail to see it. Only 

 those who have had much experience 

 with microscopic demonstration know 

 how prone the student is to see any- 

 thing and everything in the field but 

 the particular point one is calling to his 

 attention. 



By pursuing this plan, briefly outlined, 

 it seems to me that we get from our stu- 

 dents what ought to be considered as 

 satisfactory results in this branch of 

 their general work. 



APPARATUS. 



[Translation from Central-Blatt f. Bakteriologie.] 



A New Filtering Apparatus. 



From the Hygienic Laboratory of the University of 

 Michigan, Ann Arbor, Mich. 



Dr. F. G. Now. 



Although various bacteria filters have 

 been described, it may not be without 

 value to present a piece of apparatus 

 which has been in use in this hygienic 

 laboratory for some time. Besides its 

 cheapness and simplicity, it has the ad- 

 vantage that the positive pressure of 

 compressed air and the negative pressure 

 of the exhaust pump act simultaneous- 

 ly on the fluid -which is to be flltered. 

 Figure 1 shows the complete apparatus. 



The important part of the filter con- 

 sists of a glass cylinder, 20 cm. long, 

 having throughout its entire length an 

 internal diameter of 3 cm At one end 

 there is a spherical enlargement of 250 

 or 500 ccm. capacity, which is provided 

 at its upper end with a neck of about 2 

 cm. diameter. The other end of the 



