184 LABORATORY WORK ON GASTRIC DIGESTION. [BOOK II. 



Method. The directions for carrying out, which follow, are quoted 

 verbatim from those drawn up by Mr Langley for the use of his Ad- 

 vanced Practical Class. 



" Wash freshly collected fibrin in a stream of water flowing from 

 a tap for 5 or 10 minutes and chop into small pieces; place them 

 in a large quantity of water until the next day, when any pieces 

 which are still coloured with haemoglobin, or which have clumps of 

 fatty matter adhering to them, should be thrown away. 



" Place the fibrin in carmine prepared thus : to 1 grm. of carmine 

 add 1 c.c. of ammonia, mix well and add 400 c.c. of water, and stir. 

 If the mixture smells strongly of ammonia it should be placed aside 

 until it ceases to do so. 



" The fibrin should be steeped in the carmine solution for a day ; 

 when the carmine solution should be poured off and the fibrin well 

 washed in water. (Unless the quantity of fibrin placed in the carmine 

 solution has been very large, the latter may serve again.) The fibrin 

 is then ready for use. To preserve it, it is thoroughly pressed so as 

 to squeeze out the water, and then placed in a bottle with a small 

 quantity of ether, which is shaken up with it. By the action of the 

 ether the fibrin becomes somewhat less soluble in gastric juice than 

 when fresh, but it is still readily dissolved. Before the fibrin is used 

 the ether should be washed away with water. When it gives up 

 more than a trace of colour to dilute hydrochloric acid, on warming, 

 it should be thrown away. 



" When an experiment is to be made, a small quantity of the 

 stained fibrin should be placed in about five times its volume of HC1 

 (0*02 per cent.) at about 35C.; in 30 to 60 minutes it will have 

 swollen up ; the excess of acid should then be poured off, and equal 

 quantities of fibrin measured out in glass tubes containing exactly 1, 

 2, or more c.c. as required. 



" Having then added the same quantity of fibrin to equal bulks of 

 the acid and pepsin containing extracts, a small difference in the 

 amount of fibrin dissolved, i.e. in the pepsin content of the fluids, is 

 shewn by their different tints. A convenient way of writing down 

 the results for future reference is to note every five minutes which 

 numbers of a series of standard carmine solutions have the same tint 

 as the several digesting mixtures. The digesting mixtures must of 

 course be shaken before they are compared with the standard solu- 

 tions. 



" The standard carmine solutions are thus prepared : 



"To O'l gram, carmine add from burette O'l c.c. of ammonia, mix 

 well, and add 100 c.c. of glycerin. Put into a stoppered bottle and 

 keep in the dark. 



" To 6 c.c. of the O'l p. c. carmine solution add 54 c.c. of water. 

 To the test tubes add 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 c.c. respectively 

 of the dilute solution by carmine, filling up each test tube to 

 20 c.c. with water. Thus the test tubes contain respectively O'l, 

 0'2 1 c.c. of the original carmine solution. The colour of these 



