Donaldson and Hoke, Medullary Sheath. i i 



Specimen 36. Gv&y Yoy. {Urocvon c/mro-nr<^entatus), body-weight 3940 grms., 



Dr. Hardesty, San Francisco. 

 Specimen 37. Shepherd Dog, male. 



Specimen 38. Wild Cat (Feiis rufus), body-weight 3050 grms., Dr. Har- 

 desty, San Francisco. 

 Specimen 39. Cat {Felis ,io))icsticus) , male. 

 Specimen 40. Manila Monkey {.Macacus cynomolgtcs), body- weight 965 



grms., Dr. Hardesty, San Francisco. 

 Specimen 41. Spider Monkey (A(eles paniscus), body-weight 1650 grms., 



Dr. Hardesty, San Francisco. 

 Specimen 42. Rhesus Monkey {Macacus rhesus), body-weight 2720 grms. 



Dr. Hardesty, San Francisco. 

 Specimen 43. Black Coated Ape ( Macacus inuus), body-weight 5216 grms., 



Dr. Hardesty, San Francisco. 

 Specimen 44. Baboon {Cynofe/>halus bahuin), body-weight 6247 grms.. Dr. 



Hardesty, San Francisco. 

 Speciman 45. Man, adult, sciatic nerve. 



Accuracy of Measurements and Sources of Error. — In esti- 

 mating the value of the measurements given in Table VI, it is 

 to be remembered that with the magnification most commonly 

 used for the larger fibers, one-tenth of a division of the ocular 

 micrometer or o. 306 ft was a shade over 3 5^ of the diameter of 

 a fiber 10 [j. m thickness. In case, therefore, that a fiber was 

 measured as 9.7 ijl or 10.3 // instead of 10 //, the deviation in 

 the resulting aicas from that based on 10 a would be approxi- 

 mately, ± 6%. Individual cases might, therefore, readily 

 vary by this amount as an error of observation. 



With fibers of greater diameter the relative value of this 

 error would decrease, while with those of less diameter it would 

 increase. Similarly with the higher magnification used for the 

 smaller fibers, the value of the one division of the ocular micro- 

 meter was 1.42 /i, and one-tenth, or 0.142 a would be 3 % of 

 a fiber 4.7 ti in diameter. In this case also the error of one- 

 tenth of a division in the reading, either plus or minus, would 

 give rise to corresponding deviations in the resultant areas, 

 with a relative decrease as the fibers become larger and an in- 

 crease as they become smaller. 



In general, therefore, the errors of observation would in- 

 crease as the fibers diminished in diameter. Such errors, how- 

 ever, would tend in all cases to balance out and so be reduced 

 as the number of observations becomes large. 



