'////: f '/:/,/,. Kil 



celloidin in absolute alcohol and ether thin enough to flow 

 easily into the vessels. Various granular pigment.- can he 

 added. 



(0) Agar-agar is used in the same way as celloidin. A very 

 dilute solution (2-5 per cent) in water is best. 



(7) Wood 9 8 metal is a composition which has a very low 

 melting-point and can be injected into the blood-vessels. By 

 dissolving away the tissue from these, a cast of the vessels can 

 be obtained. 



(8) Methylene-blue, luematoxylin, silver nitrate, osmic acid, 

 and other fluids are used for special purposes. 



Tissues which have been injected should be hardened im- 

 mediately. Thick sections (50 u +) are the most instructive 

 in the majority of cases. Celloidin and agar injections can be 

 digested with hydrochloric acid and pepsin and a complete 

 model of the blood-vessels obtained. 



SPECIAL MICROSCOPIC TECHNIQUE. 



1. THE CELL. 



1. For the study of protoplasmic movements, one may use 

 the fine hairs of Tradesman tin cirginica, which can be obtained 

 from the freshly opened flower. These should be examined in 

 water with high powers. 



2. Amoeboid movements may be observed in the amoeba or 

 in the living white blood-corpuscles of cold-blooded animals. 



3. The inner xh-iictnrc of cells should be studied in fixed 

 specimens. Flemm ing's, Hermann's, and Zenker's fluids are 

 the most useful. Osmic acid is also of use, especially in 

 Kolossow's method (see Epithelium). Cells are stained best 

 with safranin, Heidenhain's hamiatoxylin-iron-alum, Khrlich- 

 IJiondi's triple stain, nigrosin, methylene-blue. etc. 



4. A classical object for the demonstration of ////Vox/x can 

 be obtained in June and July from frog, triton, and salamander 

 larvae. The outer skin, ova, etc., are sectioned and stained 

 with safranin or iron haematoxylin. Excellent specimens can 

 be gained from sections of a young growing onion top, or the 

 growing point of any young plant (c. y., lily). 



26 



