centrifugation . Centrifuglng for 25 to 30 min- 

 utes at 3000 rpm is entirely satisfactory. It is 

 recommended, however, that whenever possible 

 a special microhematocrit centrifuge with a 

 head especially designed for capillaries be used. 

 Such centrifuges have a speed of about 12,000 

 rpm ., hold up to 24 capillaries, and are run 

 for 4.5 to 5 minutes. 



9. Unless capillaries are properly sealed 

 blood may be lost . To guard against loss, the 

 total length of blood column in each capillary 

 should be measured with an accuracy of 1 or 

 even 0.5 mm, and recorded before centrifuglng; 

 after centrifugation it should be re -measured. 

 If the column of cells plus plasma is 1 mm short- 

 er than before centrifuglng, some blood has been 

 lost and the capillary should be discarded. 



10. As soon as the centrifuge is stopped, 

 capillaries should be removed, placed in vertic- 

 al position and read. If no loss of blood has 

 occurred, the length of the column of packed red 

 cells and the total length of the column made of 

 blood cells and plasma should be measured as 

 accurately as possible. The very thin, grayish- 

 white layer of leucocytes on the top of the 

 erythrocytes should not be measured if it is less 

 than 1 mm thick. If greater than that it may in- 

 dicate pathologic conditions and it should be 

 measured and recorded. 



There are many types of commercially 

 available hematocrit readers. Entirely satis- 

 factory results can be obtained with inexpensive 

 ruled plastic readers or a millimeter scale. 



SUMMARY 



The hematocrit value is the percentage of 

 packed red blood cells in an examined sample of 

 whole blood treated with an effective anticoagu- 

 lant. Hematocrit has a wide application in 

 clinical hematology of humans and animals . 

 Microhematocrits performed with three species 

 of trout at the Leetqwn hatchery gave the follow- 

 ing mean readings: brook trout 45 to 50; brown 

 trout 39 to 44; rainbow trout 45 to 53 . The cor- 

 relation between the hematocrit, red cell counts 

 and hemoglobin is as good in trout as in humans 

 and other vertebrates. Hematocrit readings ob- 

 tained in heparinized capillaries are 7 to 18 

 percent higher if compared with hematocrits 



obtained with blood treated with anticoagulants 

 before filling capillaries. A detailed description 

 of the microhematocrit procedure as applied to 

 trout blood is Included. 



ACKNOWLEDGMENT 



The author wishes to thank Dr . Ken 

 Wolf of this laboratory for a critical review of 

 this paper. 



LITERATURE CITED 



Adrianov, W. B. 



1937. Versuch eines Vergleichtnden Studiume 

 am Blut der Susswasserfische. Moscow 

 University, Uchenye Zaplskl. 9: 5-16. 



Benditt; Earl, Peter Morrison, and Laurence 

 Irwing 

 1941. The blood of the Atlantic salmon 



during migration . Biological Bulletin 

 Woods Hole, 80: 429-440. 



Brown, Margaret E. (Editor) 



1957. The physiology of fishes. Two 



volumes, Academic Press, Inc., New 

 York. 



Dombrowskl, Heinz 



1953. Untersuchungen Uber das Blut des 

 Karpfens ( Cyprinus carpio L) and 

 einigar anderer SUsswasserfischarten. 

 Biol. Zentralblatt, 72: 182-195. 



Dubravko, Timet 



1956. Some hematological characteristics 

 of Adriatic fish . (In Yugoslavian) . 

 Thalassia 1: 5-31. (Biological Ab- 

 stracts 31, No. 20899, 1957). 



Field, J.B., C.A. Elvehem, andC.Juday 

 1943 . A study of the blood constituents 

 of carp and trout . Journal of 

 Biological Chemistry, 148: 261-269. 



Guest, George M . , and Vinton E . Siler 



1934. A centrifuge method for the deter- 

 mination of the volume of cells in blood. 

 Journal. of Laboratory and Clinical 

 Medicine, 19: 757-768, 



13 



