54 II. DIGESTION AND ABSORPTION OF FATS 



the plasma. More of this pseudocholinesterase was found in the white 

 fiber tracts of the human cerebrum than in the grey matter. Burgen and 

 Chapman 313 also reported both the true and the pseudoenzyme in dog brain. 

 Whittaker 309 reported that the enzyme from pigeon brain closely resembles 

 erythrocyte cholinesterase, except that the rate of hydrolysis of the ali- 

 phatic esters, where acetyl-/3-methylcholine is used as a standard, is one- 

 half to three-fourths of the value obtained with the erythrocyte enzyme. 

 It is suggested that pigeon brain, like human erythrocytes, contains a small 

 amount of ali-esterase. Little 310 has shown that the specific cholinesterase 

 activity in mouse brain homogenate can be separated into two fractions by 

 centrifugation. The fraction present in the precipitate was found to be 

 more heat-labile than that in the supernatant. The distribution was 

 shown to be a real one and not the result of intact cells in the homogenate 

 {i.e., it did not represent the presence of intra- and extracellular fractions). 

 In the later report, Little 311 demonstrated that dog brain homogenate 

 could be separated into these two cholinesterase fractions. In this case, 

 also, the cholinesterase in the precipitate was the more heat-labile. It is 

 suggested that the fraction in the supernatant may represent a larger pro- 

 portion of cholinesterase from the nerve fibers. 



In a comprehensive study of the cholinesterase content of the central 

 nervous system of eight different species representing three classes of verte- 

 brates, Lindeman 314 concluded that the cholinesterase content per cell, 

 per unit of whole mass, and per unit nuclear surface, showed a consistent 

 correlation between the activity of the enzyme and the general motor ability 

 of the animal. Tower and Elliott 315 reported a similar study on samples 

 of cerebral cortex obtained from normal unanesthetized adult mice, rats, 

 guinea pigs, rabbits, cats, dogs, monkeys, cattle, and man. It was found 

 that all components of the acetylcholine system (acetylcholine content, 

 cholinesterase activity, rate of production of free and bound acetylcholine) 

 decreased fairly regularly in the animals, in accordance with an ascending 

 order on the phylogenetic scale. It was related to the average total brain 

 weight of each species, and was the same function of the brain weight for all 

 types of activity measured. The decrease in the average number of 

 neurons per unit volume of cortex with increasing brain weight was shown 

 to run parallel to the decrease in activity of the acetylcholine system. 



Wide variations in cholinesterase are to be noted in different parts of the 

 brain; this phenomenon has been reported for human, elephant, ox, dog, 



313 A. S. V. Burgen and L. M. Chipman, J. Physiol., 114, 296-305 (1951). 



314 V. F. Lindeman, Am. J. Physiol., US, 687-691 (1945). 



315 D. B. Tower and K. A. C. Elliott, Am. J. Physiol, 168, 747-759 (1952). 



