THE BLOOD. 45 



glass should press on them. Some little mechanical dexterity 

 is required to get them in position, and they are apt, after using, 

 to become so charged that their action upon the corpuscles 

 commences before they are connected with the battery. The 

 phenomena at the negative pole are those of an acid ; at the 

 positive, those of an alkali. At a distance from the line of the 

 current, secondary changes occur of a less regular character. 



Harting has devised an apparatus which is somewhat more 

 elaborate, but in principle the same. 



Other changes in the red corpuscles. If a drop of blood be 

 taken from the finger, by pricking with a needle (the triangu- 

 lar or glover's is the best), it will be seen 

 after a time that the exterior of the corpus- 

 cle is indented or crenated, as this change 

 is called. It is well shown in Fig. 20. 



Examination of the circulation in the 

 web of a frog's foot. Take a medium-sized 

 frog and curarize him by injecting beneath Plo 2 o -Human 

 the skin, with an ordinary hypodermic syr- d t v*** crenated - < R 

 inge, two drops of a weak solution of curara 

 (12,000 in water) or a few minims of a 50 per cent, solution 

 of chloral hydrate (Schaefer). After a variable time the ani- 

 mal will be completely paralyzed, but the circulation will go 

 on as before. 



There are many difficulties in the use of curara, depending on the variable 

 strength of the drug, the idiosyncrasies of the animal, and other causes that 

 we do not appear to understand. A solution which will produce a proper 

 amount of paralysis in a frog on one day will rapidly kill another frog the next 

 day. To ensure any reliability of action, it is well to have a specimen of 

 which the strength has been properly tested. Then, if time enough is at one's 

 disposal, a weak solution, such as the above, may be injected every hour until 

 the symptoms of the drug are apparent. If the subsequent recovery of the 

 animal is not of vital importance, the amount may be increased, for the circu- 

 lation will often be well shown, even if the animal does not eventually survive. 



My friend, Dr. W. H. Welch, who is in charge of the Histological Labora- 

 tory at the Bellevue Medical College, employs a watery solution of curara. 

 He keeps on hand a | per cent, solution of the drug ( 1 gramme to 200 c.c. of 

 distilled water), and then dilutes it as occasion may warrant to i per cent., or 

 even -^ per cent. (1500 or 11,000). Of this diluted solution he injects four 

 or five drops into the dorsal lymph- sac of the frog. A still more dilute solu- 

 tion he is often in the habit of using, so that the frog does not come under the 

 influence of the drug for an hour or an hour and a half. After twenty-four to 



