. The biology of the protozoa. Protozoa; Protozoa. INTRODUCTION 27 to be picked up with forceps (Porospora gigantea, a gregarine, up to 16 mm.) and many of the larger ciliates are easily visible to the unaided eye (Bursaria truncatella, Spirostomum ambiguum) while many smaller types can be seen by the trained eye as mere white specks which, in some cases, may be identified by their characteris- tic movements (e. g., Paramecium, Frontonia, Dileptus, Amphileptus, Loxophyllum, etc.). At the other extreme in size are types which are barely visible even with the most powerful lenses of the micro- s
. The biology of the protozoa. Protozoa; Protozoa. INTRODUCTION 27 to be picked up with forceps (Porospora gigantea, a gregarine, up to 16 mm.) and many of the larger ciliates are easily visible to the unaided eye (Bursaria truncatella, Spirostomum ambiguum) while many smaller types can be seen by the trained eye as mere white specks which, in some cases, may be identified by their characteris- tic movements (e. g., Paramecium, Frontonia, Dileptus, Amphileptus, Loxophyllum, etc.). At the other extreme in size are types which are barely visible even with the most powerful lenses of the micro- scope. From 8 to 16 such forms have ample room for existence in a red blood corpuscle (Babesia canis), or 200 to 300 may live simulta- neously in a single infected liver or spleen cell of man (Leishmania. B k Fig. G.—Dileptus gigas, two sister cells. A, normal individual; B, individual starved for several days. (From Calkins.) donovani). Between these two extremes of size lie the majority of Protozoa. Their measurements are usually expressed in terms of " microns " or thousandth parts of a millimeter which are represented by the symbol n, each micron being 2t|-oo- °^ an ^ncn- Thus Leish- mania donovani measures from 2 n to 4 /x, Paramecium caudatum upward of 200 //, Bursaria truncatella, 1500 /x, etc. The same species frequently shows remarkable variations in size due to environmental conditions or to different stages in the life history. Thus normal specimens of Paramecium caudatum may measure from 175 /j, to 250 /x when fully grown and similar variations are characteristic of all species. Environmental factors, especially. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Calkins, Gary N. (Gary Nathan), b. 1869. Philadelphia, Lea & Febiger
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