THE CAPILLARY CIRCULATION. 



347 



ness with which the circulation may be maintained even in the internal 

 organs, exposed at ordinary temperatures. In order to secure immo- 

 bility, the medulla oblongata may first be broken up by a strong needle 

 introduced through the cranium, or the voluntary muscles may be para- 

 lyzed by the subcutaneous injection of six drops of a filtered watery 

 solution of woorara, made in the proportion of one part to five hundred. 

 The whole body, with the exception of the part used for observation, 

 should be enveloped in a light linen or cotton bandage, kept moistened 

 to prevent desiccation of the surface. The tongue, or the web of one 

 foot, may be stretched over a glass side, and placed under the lens of 

 the instrument. To examine the pulmonary circulation, an opening 

 should be made in one side just behind the anterior limb, and the 

 lung moderately inflated through the glottis, until it protrudes through 

 the external wound. For the mesenteric circulation, an incision should 

 be made in the left flank of a male frog, a loop of intestine carefully 

 drawn out of the abdomen, and the mesentery allowed to rest upon a 

 circular glass plate, 12 millimetres in diameter, and 6 millimetres in 

 thickness, cemented upon a large glass plate, by which the body of the 

 animal is supported. Under favorable circumstances the circulation 

 will go on in either of these organs for several hours. 



When the circulation is examined in this manner, the smaller arte- 

 ries, the capillary vessels, and the minute veins are often -visible under 

 the microscope in the same 

 region. The blood can be 

 seen entering the field by 

 the smaller arteries, shooting 

 through them with great ra- 

 pidity in successive impulses, 

 and flowing off by the veins 

 at a somewhat slower rate. 

 In the capillaries, the circula- 

 tion is considerably less rapid 

 than in either the arteries or 

 the veins. It is also perfectly 

 steady and uninterrupted in 

 its flow. The blood moves 

 through its vascular channels 

 in a uniform current, without 

 their exhibiting any appear- 

 ance of contraction or dilata- 

 tion. Another marked peculiarity of the capillary circulation is that 

 it has no definite direction. Its numerous streams pass indifferently 

 above and below each other, at right angles to each other's course, or 

 even in opposite directions ; so that the blood, while in the capillaries, 

 circulates everywhere among the tissues, in such a manner as to be 

 distributed to all parts of their substance. 



The motion of the red and white globules is also peculiar, and shows 



CAPILLARY CIRCULATION in web of frog's foot. 



