Abstract
This problem was undertaken for three reasons. (1) There are no well controlled experiments, so far as I know, in which an aquatic form has been subjected to a constant low pressure and examined for changes in its blood picture. Necturus was chosen as the experimental animal because of the readily available source of blood in the afferent branchial arteries of the external gills and because the normal blood picture has been thoroughly worked out by Dawson. 1 (2) Experiments such as those described below supply a method for determining the nature of the red cell ancestors in Necturus by causing them to leave the erythrocytopoietic loci and enter the circulating blood. (3) It is interesting to compare the intensity and duration of the stimulus required to send out erythroid cells into the blood stream of an aquatic form with the intensity and duration necessary to evoke an analogous response in mammals (i. e., increase the reticulocyte and total red cell count).
Groups of Necturi were placed in jars of water and subjected to a constant pressure of 330 mm. Hg. in a specially devised low pressure chamber for varying periods up to 9 weeks of continuous exposure. (For the construction of the apparatus, see Dubin. 2 ) The animals were removed once a day for about an hour, and the water in which they were kept was replaced by fresh water. All animals, including the controls, were fed live earthworms twice weekly. In order to minimize the effects of hemorrhage, the small quantity of blood necessary for total counts and 2 smears was drawn on 2 occasions only, once, before the animals were placed in the tank, and later, when they were examined to determine the effects of the reduced pressure.
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