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HANDBOOK OF PHYSIOLOGY 



CIRCULATION II 



lights have made this site a popular one, especially for 

 observing changes in vascular patterns and flow in 

 diseases in humans. Specific instructions for its use 

 can be found in papers by Bloch (15), Grafflin & 

 Corddry (56), and Lee (76). 



The type of microscopic and lighting equipment, 

 as well as the position of the patient (supine or up- 

 right), varies with the investigator, but, generally, 

 compound microscopes, routine ophthalmological 

 supports, and lights of moderate intensity constitute 

 the basic components. 



Bloch (13) notes that the walls of the blood vessels 

 are not clearly seen because of the use of oblique 

 illumination, although a moving column of blood 

 can be clearly seen against the white background of 

 the sclera. Other limitations are that optical resolu- 

 tion is lost by the patient's inability to hold the eye 

 still, edema, highlights due to lacrimation, and 

 excessive abnormal pigmentation in some cases. 

 Very high magnification is difficult because of move- 

 ments of the eyeball and the inability of the patient to 

 tolerate light of high intensity. Also, high power 

 objectives must be too close to the eyeball if they are 

 to be in focus. 



The advantages of the technique are that blood 

 vessels in an unanesthetized human can be readily 

 observed without any surgical intervention or any 

 preparation to render the vascular beds visible. 

 Tears supply the proper irrigation for this membra- 

 nous tissue. An entire vascular field can be studied 

 again and again in the same subject, and blood flow 

 can be followed from arteriole through capillary to 

 venule. 



Rat Mesoappendix 



The technique for microscopic observation of 

 mesenteric structures, as described in detail by Zwei- 

 fach (145), has been used by him in studies on dog 

 omentum and mesenteric structures in several ani- 

 mals, but primarily in the cecal mesentery (mesoce- 

 cum) of the rat. 



Preparation of this tissue consists of exteriorizing 

 the cecum of the anesthetized rat and then spreading 

 the mesentery, which lies between the cecum and the 

 terminal ileum, for observation. The mesentery is 

 continuously irrigated with a warm Ringer's gelatin 

 solution. 



Zweifach (147) believes that the advantages of 

 using this terminal vascular bed are: a) the accessibil- 

 ity of the vessels for direct stimulation by mechanical, 

 chemical, or electrical means; b) clarity of visualiza- 



tion; r) minimum interference by surgical procedures 

 to normal vascular behavior; d) adequate display of 

 the entire extent of the terminal vascular bed. 



The disadvantages include those which apply to 

 any technique using anesthetized animals subjected 

 to surgical procedures to expose the tissue for observa- 

 tion. An idea of the lability of this vascular bed may 

 be obtained by reading the precautions to be taken in 

 using the rat mesoappendix for bioassay (1 53). 



Bat Wing 



Microscopic observations of vascular structures in 

 the bat wing, a comparatively old technique (68), 

 was revived by Nicoll & Webb (88) in 1946. A de- 

 scription of the preparation and current uses may be 

 found in papers by Webb & Nicoll (130) and Wiede- 

 man (136). 



An unanesthetized animal is slipped into a holder 

 that allows the wings, lightly held by spring clips, to 

 be extended over a glass plate. Magnifications up to 

 2500 times can be used with good resolution. 



The simplicity of the preparation is one of its great 

 advantages, coupled with the elimination of anesthesia 

 and surgery which permits observation without dis- 

 turbing the normal circulation or subjecting the 

 animal to undue stress. The blood vessels and lym- 

 phatics are accessible for cannulation which permits 

 perfusion of drugs or measurements of pressure, and 

 the nerves can be readily stimulated or sectioned. Also, 

 in this mammal the two wings can be used simulta- 

 neously, which allows one for control and the other 

 for experimental procedures. 



One undesirable feature is the difficulty in obtaining 

 bats during the entire year, and, because the animals 

 will not eat in captivity, their survival time in the 

 laboratory is limited to a few months. Also, histological 

 sections are difficult to prepare for study because of 

 the extreme thinness of the wing. 



Utilization of these various techniques has resulted 

 in the resolution of some old controversies, e.g., the 

 role of the Rouget cell, and has clarified to some ex- 

 tent the anatomical structure and physiological func- 

 tion of terminal vascular beds. It has made many 

 investigators aware of the danger of ascribing specific 

 changes in blood pressure or the rate or volume of 

 blood flow to the activity of small blood vessels, on the 

 basis of indirect measurements. While the change 

 in systemic pressure following some experimen- 

 tal procedure need not be challenged, the means by 

 which it is brought about may be better explained 



