Blood Pressure and Blood Protein Determinations in the Frog.

Abstract

In a previous note, 1 the authors called attention to the low protein content of frog's blood. The low colloidal pressure of the blood is an important factor in determining the production of urine. The blood pressure of the frog is not nearly as high as in mammals, but if filtration is the basis of glomerular activity, there should be enough pressure to overcome the osmotic pressure of the colloids of the frog's blood.

It seemed desirable, therefore, to make some actual blood pressure determinations and determinations of the protein content of the blood on the same animal.

In order to make blood pressure determinations on the intact animal, the following apparatus was devised. A modified apparatus such as is used for determining arterial blood pressure in man was used. Small rubber cuffs were constructed from small rubber balloons, varying in size from one-half to one inch wide, and 3 to 5 inches long. A rubber tube was cemented into the open end of the balloon and by means of it the balloon was connected to a mercury manometer, an outlet valve, a Woolf bottle to act as a buffer, and a rubber atomizer bulb. The frog was placed in a suitably sized box with its right leg protruding through a small opening. The rubber cuff was then wrapped around the thigh or leg, the web of the foot placed under the low power of the microscope and as large an arteriole as could be found was brought into focus. A pulsating stream could be observed. The pressure in the cuff recorded by the mercury manometer was raised until pulsations in the arteriole could no longer be seen. The air was then gradually let out of the system and when pulsations first were observed, the mercury manometer was read for systolic pressure. As the pressure continued to fall slowly, it was noticed that between systolic peaks of pressure, the blood stream slowed to complete stoppage and sometimes to a reverse flow. When this reverse flow disappeared and the stoppage between systoles began to disappear, the diastolic pressure was taken. The readings obtained in this manner have been checked up with a mercury manometer attached directly to an artery in the abdominal cavity and with a Hurthle manometer attached in the same manner, and the readings were found to be within the limit of error.