ARSENIC 



28 



ARTERIOVENOUS ANASTOMOSES 



The distribution to the several tissues 

 of radioactive arsenic injected intra- 

 venously into rabbits as sodium arsenate 

 has been investigated by duPont, O., 

 Irving, A. and Warren, S. L., Am. J. 

 Syph. etc., 1942, 26, 96-118. It is impor- 

 tant to determine whether the results 

 conform with those given by the micro- 

 chemical techniques. 



Arsphenamines. The specificity of the 

 silver reaction of Jancs6, N., Ztschr. 

 f. d. Ges. exper. Med., 1929,65, 98 is 

 questioned bv Gomori, G., J. Mt. 

 Sinai Hosp., 1944-45, 11, 317-326 since 

 it may demonstrate other reducing sub- 

 stances beside the arsphenamines. 



Artefacts, see Artifacts. 



Arteries. If one wishes an elastic artery 

 take a large trunk near the heart such as 

 the aorta, innominate or subclavian; if, 

 on the other hand, a typical muscular 

 artery is required select one further 

 afield like the radial or external carotid. 

 Arterial walls are seldom examined 

 microscopically in vivo because they are 

 relatively large and difficult to get at 

 without injury. An exception in man is 

 the retinal artery which can be seen 

 by ophthalmoscopic examination. To 

 closely observe excised pieces of arteries 

 is all too fi'equently neglected. The 

 tissue elements are so tightly bound to- 

 gether that to tease them apart for study 

 at high magnification is rather unsatis- 

 factory. However, when the adventitial 

 adipose and connective tissue is stripped 

 off from a fresh specimen, the remainder 

 of the wall can very advantageously he 

 made translucent by treatment with 

 pure glycerin for 1-2 hrs. as described 

 by Winternitz, M. C., Thomas, R. M. 

 and LeCompte, P. M. in their book "The 

 Biology of Arteriosclerosis", Spring- 

 field: Thomas, 1938, 142 pp. Since the 

 color of the blood is preserved within 

 the intramural vessels their arrangement 

 can be studied (see Vasa Vasorum). 

 Fatty substances can also be located 

 because they are not removed by the 

 glycerin. 



Chief reliance is ordinarily placed in 

 the appearance of arterial walls when 

 seen in sections of fixed tissue. It is 

 important to remember that, when carry- 

 ing blood during life, the lumina are 

 larger and the walls less folded than in 

 the fixed condition. The difference has 

 been graphically demonstrated by Gallo- 

 way, R. J. M., Am. J. Path., 1936, 12, 

 333-336. His figures should be exam- 

 ined. For routine purposes fixation in 

 Formalin-Zenker followed by Mallory's 

 Connective Tissue Stain supplemented 

 by Resorcin Fuchsin or Orcein for 

 elastic tissue is satisfactory. _ Special 

 methods may be needed for Lipids ; and 



for minerals, see Calcium, Iron and 

 Microincineration. Innervation, like- 

 wise, is to be studied by methods em- 

 ployed to demonstrate Nerve Endings 

 in other tissues. See Vasa Vasorum. 

 Much literature on techniques is given 

 by various authors in Cowdry, E. V., 

 Arteriosclerosis, New York: Macmillan, 

 1933, 617 pp. The investigation of 

 arterial walls is apt to be one sided 

 limited only to structure and composi- 

 tion demonstrated microscopically. It 

 is high time that these lines of study 

 are supplemented by accurate meas- 

 urement of the physical properties of 

 pulse wave velocity, sound production, 

 elasticity and so on of the same vessels 

 by methods described by Bramwell in 

 the above mentioned volume. 



Arterioles, capillaries and venules, in con- 

 trast to the much larger arteries and 

 veins, can readily be examined in experi- 

 mental animals microscopically in the 

 living state. Since they are linked 

 together a single preparation by Sandi- 

 son's rabbit ear method shows all three, 

 or they may be viewed in the living 

 tadpole's tail or other transparent tissue 

 of lower forms. For convenience, how- 

 ever, it seems best to briefly mention 

 the microscopic techniques for each 

 separately. There is much to choose 

 from. Information is frequently de- 

 manded on the condition of the arterio- 

 lar walls. This can best be supplied 

 by staining paraffin sections of Forma- 

 lin-Zenker fixed material with Mal- 

 lory's Connective Tissue stain or with 

 Masson's Trichrome stain which is 

 closely related to it. Weigert's Re- 

 sorcin Fuchsin is satisfactory for elastic 

 tissue. The Silver Citrate technique is 

 capable of yielding valuable data on arte- 

 rioles and capillaries. Because arte- 

 rioles contain a higher percentage of 

 muscle than any other blood vessel their 

 appearance will vary greatly with the 

 degree of contraction or relaxation of 

 muscle. According to Kernohan, J. W., 

 Anderson, E. W. and Keith, N. M., 

 Arch. Int. Med., 1929, 44, 395-423 in 

 fixed preparations from normal persons 

 the average ratio of thickness of arteriolar 

 wall to width of lumen is 1:2. 



Arteriovenous Anastomoses are direct con- 

 nections between arteries and veins 

 without intervening capillaries. No 

 special histological technique is required 

 for their demonstration in sections but 

 one should look for them where they are 

 particularly numerous, as in rabbits at 

 the tip of the nose (diameter, 80-100^) 

 and in humans in the palms of the hands, 

 the soles of the feet and near the ends 

 of the fingers where their diameter is 



