ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 783 



with carbol-f uchsin f or 15 to 2o minutes in the cold, and then the super- 

 fluous fluid is drained off. Pappenheim's stain is then applied until the 

 preparation is blue ; the slide is then washed, dried, and mounted in 

 balsam. Pappenheim's stain consists of 1 p.c. rosalic acid in absolute 

 alcohol, to which is added methylen-blue to saturation and a small 

 quantity of glycerin. The smears from fasces should be thin ; milk 

 should be centrif uged, and the fat removed by means of ether. 



Staining 1 Blood Platelets.*— J. Homer Wright demonstrated the 

 histogenesis of the blood platelets by the following procedure. The 

 material should be obtained immediately after death or taken from 

 the living animal. For fixation methyl-alcohol, formaldehyde, or a 

 saturated solution of mercuric chloride in a 0*9 p.c. solution of sodium 

 chloride, may be used. Methyl-alcohol is not now recommended for 

 fixation. Formaldehyde should not be allowed to act longer than 

 48 hours. The method is not applicable to material fixed in Zenker's 

 fluid. The tissue is dehydrated by alcohol followed by acetone, cleared 

 in thick oil of cedar followed by xylol, and imbedded in paraffin. The 

 sections should not be more than 4/x in thickness. Crystals of corrosive 

 sublimate in the sections are to be removed by treatment with Gram's 

 solution of iodine and alcohol. The sections are stained while affixed 

 to the slide by Meyer's glycerin-albumin mixture. The staining fluid 

 and the mode of its preparation are described below. 



The staining, clearing and mounting is carried out as follows :— 

 1. Equal parts of the staining fluid and distilled water are mixed in 

 a small wine glass and immediately poured on to the slide. The 

 measuring is conveniently done by means of a small pipette provided 

 with a rubber bulb. At least 2 c.cm. of the freshly diluted staining 

 fluid are thus spread out over the slide, which should be supported upon 

 some object in such a way as to prevent the fluid from running off. 

 The spreading out of the fluid in a layer is important, because it 

 facilitates the evaporation of the alcohol whereby the staining elements 

 slowly precipitate out of solution and, while doing so, stain the tissue 

 elements. This precipitate appears as a yellowish metallic scum which 

 slowly forms on the surface of the mixture. The diluted staining fluid 

 is allowed to act for about 10 minutes, when the preparation is im- 

 mediately washed in water. The exact time required for the best 

 results has to be determined for each batch of the staining fluid. The 

 proper staining of the preparation may be judged by examining it by a 

 yellowish artificial light under a low magnifying power, after pouring 

 back the diluted staining fluid into the wine glass. The stain is to be 

 regarded as sufficiently intense and the staining process stopped by 

 washing the preparation in water when the cytoplasm of the giant cells 

 has acquired a bright red colour and the fibrils of the reticulum begin 

 to take on a red colour also. If the staining is found not sufficiently 

 intense the diluted staining fluid is poured back on the preparation and 

 allowed to act longer. Over-staining and the formation of a black-red 

 granular precipitate on the preparation occur if the diluted staining 

 fluid is allowed to act longer than a certain time. 



* Publications of the Massachusetts General Hospital, iii. (1910) pp. 1-16 

 (2 pis.). 



