336 SUMMARY AND CONCLUSIONS. 



also studied. It has been generally stated in the zoologies that the white 

 rat is an albino of the black rat. From our examination of its crystals it 

 is evident that the white rat is closely related to the brown or Norway rat, 

 but it can not be closely related to the black or Alexandrine rats. On the 

 other hand, the black and Alexandrine rats are very closely related to each 

 other, but are probably distinct varieties of the same species. 



Unfortunately (for phylogenetic studies) the species examined were 

 not as a rule those which might be regarded as forms of which the origin 

 was very uncertain, and but few examples of the bearing of this method 

 of research upon the tracing of the phylogeny of species are to be found 

 in the list of species examined. Enough examples have, however, been 

 enumerated to show the application of this method to the study of phy- 

 logenetic and zoological relationships and to demonstrate its value. 



THE INFLUENCE OF CERTAIN PHYSIOLOGICAL CONDITIONS UPON THE 

 COMPOSITION AND COLORING MATTER OF THE BLOOD. 



The normal coloring matter of vertebrate blood may be regarded as 

 being a mixture of variable amounts of oxyhemoglobin, reduced hemo- 

 globin, metoxyhemoglobin, methemoglobin, etc. The percentages of these 

 substances vary with the activity or inactivity of the animal, with the 

 amount of oxygen and carbon dioxide in the blood, and with the intensity 

 of oxidation and other conditions. These in turn are conditioned, in part 

 at least, by food and environment. 



Hibernating animals seem to have a relatively large proportion of 

 the hemoglobin in the form of metoxyhemoglobin, which seems to be an 

 inert, resting stage of this substance, neither taking up nor giving off oxygen 

 very readily. The bears, for example, show a large proportion of this sub- 

 stance in their blood, and the blood has a brownish color. In most of the 

 rodents the oxyhemoglobin changes readily to metoxyhemoglobin upon 

 standing, at least in the covered preparations. A similar condition is prob- 

 ably to be found in the shad during the breeding season, when the fish 

 does not feed. The shad caught in our rivers during the spawning season 

 show a large proportion of metoxyhemoglobin in their blood, if the blood 

 is obtained from the living fish. It may, however, change to oxyhemoglobin 

 in case of fish that have been exposed to the air in the market. As less 

 oxygen is required for the physiological processes of the fish during this 

 time when it is not feeding, it is reasonable to suppose that a part of the 

 hemoglobin is converted into this more or less inert, modified form, during 

 this period. 



Among the cats, the American species show a much larger percentage 

 of oxyhemoglobin in their blood, or at least crystals of this substance develop 

 much more readily in their blood, than in the blood of the species of the 

 Old World cats. In the lion, tiger, leopard-cat, and common cat of the Old 

 World cats, the first crystals to appear are reduced hemoglobin, and the 

 oxyhemoglobin is produced with some difficulty or by further oxidation of 

 the blood. But in the wild cat, mountain-lion, jaguar, and the lynx the 

 oxyhemoglobin crystals form readily as a first crop in the fresh blood. 



