62 CIRCULATORY SYSTEM. 



(ff) The clot will show delicate filaments forming a con- 

 fused network of radiating and intercrossing threads often of 

 great fineness. Clusters of granules occur frequently at the 

 points of radiation. Blood platelets ? 



Haemoglobin crystals. Rat or guinea-pig. Mix a drop of blood 

 on a slide with the same quantity of water, cover and watch for the 

 appearance of crystals, first near the edge of the cover. When well 

 developed remove the cover, dry thoroughly, replace the cover and 

 cement it with a thin edging of glycerin jelly, covered when dry with 

 gold size. 



crystals. To a drop of your own blood on a slide add 

 a small grain of chloride of sodium, nearly dry it, cover and add some 

 glacial acetic acid arid heat over the bunsen flame until bubbles are 

 freely given off. Repeat the heating if the crystals do not appear. Dry 

 the preparation completely, add balsam, and cover. 



Examine (//) for crystals, which will gradually form, appear- 

 ing at first as nearly black, fine, short needles, often in 

 clusters. 



The Circulation. May be studied in any of the following : 



"Web of the frog's foot. Use a piece of cotton cloth six inches 

 square with a hole in the centre. Wet the cloth, draw one hind leg 

 through the hole and wrap the remainder round the frog so as to form 

 a sack, secure the mouth with string, and place the frog upon the 

 support. Secure with ligatures around the support and frog, one round 

 the body and one encircling the knees. The frog will remain quiescent 

 if it is kept moist and is not too tightly restrained by the ligatures. To 

 the longest and one of the neighbouring toes of the foot attach soft threads, 

 lay the frog ventrally on the support and extend the web over the triangular 

 gap by securing the threads in the slits cut for the purpose. Cover the 

 extended portion of the web with a triangular piece of cover-glass. 



Frog's mesentery. In a pithed frog laid dorsally on the support 

 open the abdominal cavity by a longitudinal incision below the axilla. 

 Carefully draw out a loop of the small intestine and pin it to the semi- 

 circular cork rim on the support. Cover. 



