ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 629 



for 48 hours more. If cleared, they are immersed in upgraded glycerins. 

 If not clear, they are placed in a mixture of equal parts of 1 p.c. KHO 

 and 50 p.c. ammonium hydroxide for 5-72 hours. Next they come into 

 20 p.c. glycerin for 48 hours or more, the treatment, as outlined above, 

 being continued. 



By following this method, the systems of bones, cartilages, arteries, 

 veins, lymphatics, and various ducts, can be demonstrated in a trans- 

 parent embryo, or in large sections of adult tissue, without distortion of 

 the structures. 



For staining the skeletal system, it is advised to place the fresh 

 specimen in 95 p.c. alcohol, and then treat for 24 hours with alum 

 cochineal, and then clear with 1 p.c. potassium hydrate. 



Specimens may be mounted in the following way : Remove from pure 

 glycerin, wipe, and quickly wash. Place in a little thick gelatin, and 

 lay on a warm slide. When the gelatin has hardened, return to pure 

 glycerin. 



Microscopic Estimate of Bacteria in Milk.* — F. H. Slack advocates 

 the following method for the bacterial estimate of milk. The sample is 

 centrifuged, and the sediment of a known quantity of milk obtained is 

 emulsified with a drop or two of sterilised water and spread into even 

 smears on glass slides, previously correctly spaced with a blue pencil. 

 The observer finds a representative field seen through a -jVth oil immer- 

 sion, and regards it as a y^^th dilution plate, each coccus, bacillus, 

 etc., representing a colony on such a plate. The number of organisms 

 in the field multiplied by 10,000 gives approximately the number of 

 bacteria per c.cm. in the sample of the milk. The author claims that 

 the method is practical for certifying milk as containing less than 50,000 

 bacteria per c.cm. ; there is also advantage in the rapidity of the method, 

 and in the possibility of examining large numbers of samples without 

 delay. 



Counting Bacilli.f — W. C. Oram writes that he has found an instru- 

 ment, made for him by Alexander and Fowler, of Liverpool, very con- 

 venient in the operation of counting the bacilli engulfed by the white 

 blood corpuscles when engaged in estimating opsonic indices by Wright's 

 method. The apparatus consists of two dials — one for recording the 

 bacilli and the other the corpuscles — the dial hand moving through 

 one division of the dial for each depression of the attached pedal. 

 The instrument is intended to be placed upon the floor and worked by 

 the feet, thus leaving both hands free, the one for focusing, and the 

 other for the manipulation of the slide. When the corpuscle register 

 reaches 50, which is the usual number to observe, a bell sounds, indi- 

 cating the completion of the count, and it only remains to take the 

 reading of the other dial, which will give the number of bacilli found. 

 The instrument, he thinks, might also serve for the taking of ordinary 

 blood counts, one dial being used to register the squares of the hamio- 

 cytometer, and the other the corpuscles. 



* Technology Quarterly, xix. (1906) p. 37. 

 t Brit. Med. Journ., 1906, i., p. 1534. 



