THE INTESTINAL PROTOZOA OF FROGS AND TOADS. 205 
field’s hematoxylin. But I have used all the ordinary fixing 
fluids and stains. The greatest importance has always been 
attached to observations on the living animal. 
As the organisms described naturally live in an anaérobic 
condition they are most suitably examined under tightly 
waxed-down cover-slips, and not in hanging-drop preparations. 
It is almost impossible to obtain the contents of the frog’s 
alimentary canal when required whilst the animal remains 
alive. Therefore I have had to resort to various means for 
obtaining the necessary material. I have frequently used 
the following method: A frog is taken and its brain (but not 
its spinal cord) pithed. When it has recovered from shock 
it is, of course, still quite lively, and will live for along time. 
I pin the animal down in a dissecting dish, and by making an 
incision into the abdomen remove the contents of the large 
intestine by operating directly on it. If the frog be kept cool 
it will live for many days, thus enabling one to go on removing 
the gut contents at any required intervals of time. I have 
found the most suitable method of extracting the contents of 
the large intestine is to make a small cut into the small 
intestine at its juncture with the large. The contents of the 
large intestine can then be removed through the hole, and when 
sufficient has been extracted a piece of cotton can be tied 
immediately below the incision so as to close the large 
intestine once more. The frogs must be kept damp by 
covering them with wet cloths. 
So many different organisms are to be found in the 
intestine of the frog! and toad that it will not be out of place to 
refer to these briefly at this point. In addition to the animals 
described in detail in subsequent pages, there are the following: 
Among Protozoa we find Opalina ranarum Purk. et Val., 
Nyctotherus cordiformis Ehrenberg, Balantidium 
entozoon Khrenberg, Balantidium duodeni Stein, and 
Balantidium elongatum Stein.?, Copromonas is occa- 
* Rana temporaria L. has been especially studied. 
* First recorded by Dale (6). 
