TECHNIC (BLOOD AND BLOOD-FORMING ORGANS). 231 



plectic areas, are the hematoidin crystals first discovered by Virchow. 

 Masses of these crystals have an orange color. Microscopically, they 

 appear as red rhombic plates. As they are soluble in neither alcohol 

 nor chloroform, they are easily preserved in Canada balsam. Their 

 artificial production has as yet never been accomplished. Hematoidin 

 contains no iron. 



The fibrin thrown down when the blood coagulates may be dem- 

 onstrated upon the slide in the form of very fine particles and fila- 

 ments. A drop of blood is brought upon the slide and kept for a time in 

 a moist chamber or on the table until it begins to clot ; after which a 

 cover-slip is applied and the preparation washed with water by continued 

 irrigation. In this manner most of the red blood-corpuscles are removed. 

 Lugol solution may now be added, which stains brown the filaments of 

 the fibrin network adherent to the slide. In order to see the fibrin net- 

 work in sections, it is better to use specimens previously fixed in alcohol ; 

 the sections are stained for ten minutes in a concentrated solution of gen- 

 tian-violet in anilin water (Weigert), rinsed in normal salt solution, 

 treated for about ten minutes with iodo-iodid of potassium solution, and 

 then spread upon a slide and dried with filter-paper. They are now 

 placed in a solution consisting of 2 parts of anilin oil and i part of xylol 

 until they become perfectly transparent. This solution is then replaced 

 by pure xylol and finally by Canada balsam. The fibrin network is 

 stained a deep violet. 



Blood Current. There are different methods and a variety of mate- 

 rial at our disposal for the demonstration of the blood current through the 

 vessels. The best object for this purpose is probably the frog. The proce- 

 dure is as follows : The animal is immobilized by poisoning with curare. ^ 

 gm. of a i % aqueous solution injected into the dorsal lymph-sac will immo- 

 bilize the frog in a short time. The exact dose can not, however, be given, 

 as the commercial curare is not a uniform chemical compound ; the dose 

 must therefore be ascertained by experiment. As is well known, curare 

 affects exclusively the nerve end-organs of striated voluntary muscle, but 

 does not affect either the heart muscle or unstriated muscular tissue ; hence 

 the utility of curare for this purpose. In order to see the blood current, 

 it is only necessary to stretch the transparent web between the frog's toes 

 and fasten it with insect needles to a cork plate having a suitable open- 

 ing. If the cork plate be large enough to accommodate the whole frog, 

 it may be placed in such a position that its opening lies over that in the 

 stage of the microscope. The web thus spread out may be examined 

 with a medium magnification. The tongue of the frog is also used for the 

 same purpose. As the latter is attached to the anterior angle of the lower 

 jaw, it may be conveniently drawn out, suitably stretched, and then 

 placed over the hole in the cork plate. A very good view of the circula- 

 tion may be obtained by examining the mesentery of a frog. The migra- 

 tion of the leucocytes through the vessel-walls can also be studied in such 

 preparations. An incision 0.5 cm. in length is made in the right axillary 

 line through the skin of a frog (best in the male), care being taken not to 

 injure any vessels (which can be seen through the skin in frogs possessing 

 little pigment). The abdominal muscles are then incised and a pair of 

 forceps introduced to grasp one of the presenting intestinal loops. The 

 latter is then attached to the cork plate with needles, and the mesentery 

 carefully stretched over the opening. On examining the specimen it is 

 best to moisten it with normal salt solution and to cover the area to be 



