November 17, 1923] 



NA TURE 



725 



i 



the dogfish (/. Biol. Chem., 1921, xlv. 263), and 

 pentose compounds, which have in many cases been 

 identified as nucleotides, and are probably always 

 present as such, have been found distributed through 

 a wide range of animal tissues. 



Is it possible that the carbohydrate substance re- 

 ferred to by Messrs. Winter and Smith is of a nucleo- 

 tide nature ? The nucleotides give the a-naphthol 

 test, but there is a possibility of the pentose con- 

 stituent, to which the reaction is due, escaping notice 

 on testing a solution after acid hydrolysis for reducing 

 power, especially if only a small quantity of material 

 is available, moderately strong acid is used, and the 

 hydrolysis is carried out in an open vessel at the boiling- 

 point, since, in these circumstances, the pentose readily 

 goes over to furfurol and is lost by volatilisation. 



I hazard the suggestion for this reason. I have 

 recently found that the tissue of the islet gland in a 

 typical teleost fish {Ophiodon elongatus, Girard) is the 

 richest in pentose compounds (nucleotides) of all the 

 tissues of the body, notably richer than the zymogenous 

 pancreatic tissue. Since it has been shown that the 

 islet gland in such fishes is homologous with the isles 

 of Langerhans in the mammalian pancreas, I have 

 suggested, in a paper on the subject which is shortly 

 to appear in the Journal of Biological Chemistry , that 

 it would be justifiable to infer from this that the 

 general high pentose content of the pancreas in 

 mammals is due mainly to the presence of the isles 

 of Langerhans. 



With the view of tracing a connexion between the 

 high pentose content of the islet tissue and its func- 

 tion of insulin production, I have made use of the 

 hypothesis, put forward by Heilbron and HoUins 

 ']Rep. Brit. Ass., 1922, 396) to explain the formation 

 if compounds of the C5 series from those of the Cg 

 ries in plants, that hydroxymethyl-furfuraldehyde 

 s first formed by loss of water, and this goes over to 

 a member of the C5 series by respiratory oxidation. 

 This transformation would seem to necessitate the 

 pre-formation of an activated form of glucose, and I 

 have suggested that the plant hormone, glucokinin, 

 described by Collip {/. Biol. Chem., 1923, Ivi. 513) 

 probably performs the function of activation. 



If this is so, and pentose is formed in the animal 

 organism from activated glucose by a similar series of 

 steps as is postulated for plants, it seems to indicate a con- 

 nexion between the production of insulin and the high 

 concentration of pentose compounds in the islet tissue. 



If there is anything in this idea it may also be 

 applied to explain the production of pentose com- 

 pounds in the blood and other tissues under the action 

 of insulin, and it would be interesting in this con- 

 exion to determine whether adenine nucleotide occurs 



the blood of diabetics. C. Berkeley. 



Marine Biological Station, 



Nanaimo, British Columbia, 

 ()( (ober 15. 



An Uncommon Type of Cloud. 



There are many striking cloud phenomena which 

 may be regarded as local. While the same general 

 laws of cloud formation prevail in all climates, yet 

 some forms, while not radically different, display 

 \aryinR degrees of magnitude or intensity in certain 

 parts of the world. 



The form known as " mammato-cumulus " or 

 " festoon-cloud " or, as called in the Orkneys, " pocky 

 rloud," is of this nature, and while it occurs in a very 

 l^ronounced fashion in Australia, the United States, 

 and other countries, it is almost a very rare phenom- 

 enon in the British Isles, and then, as a rule, in a 

 very " mild " form. 



NO. 2820, VOL. I 12] 



An illustration which is usually given to represent 

 this type is that which appears in the " International 

 Cloud Atlas." It is from a negative by H. C. Russell, 

 who secured it in Sydney, Australia, in the year 1895. 

 It shows the type in its most intense form. 



Less pronounced is the illustration given by M. J, 

 Loisel in his " Atlas photographique des nuages," 

 from a negative he took at Chiavari in Italy in 1908. 



Still less pronounced is that given in the " Meteoro- 

 logical Glossary," issued by the ^leteorological Office, 

 from a negative by Capt.'Cave taken in England in 



1915- 



It may be remarked that, while almost all books on 

 meteorology refer somewhat in detail to this type of 

 cloud, it is very rare that any illustration from a 

 photograph accompanies the text. The reason for 

 this is evidently due to the fact that this type does 

 not occur very often in the British Isles, and when 

 it does the phenomenon is a fleeting one, lasting for 

 only a few minutes. Having observed and photo- 

 graphed clouds for many years, I have only seen 



this type on about six different occasions and photo- 

 graphed it on three ; even then the type was not of 

 a very pronounced nature. 



In his book entitled " Cloud Studies," the late 

 Mr. Arthur Clayden writes: " In some countries it 

 seems to be frequently observed, but in England it 

 is so uncommon that the writer has only noticed it 

 about a dozen times in twenty years, and on no one 

 of these did it last long enough to allow of its portrait 

 being taken." 



The main feature of this type of cloud is that it 

 occurs on the underneath surface of a large cumulus 

 cloud, and its appearance, in its most pronounced 

 state, is of a globular formation exhibiting a large 

 number of well - defined rounded masses of cloud 

 hanging downwards below the main cloud. The cloud 

 is generally associated with very disturbed atmospheric 

 conditions, heavy rain, and with thunderstorms. 



On October 22 last, at 12.45 p.m. G.M.T., an 

 example of this form of cloud, very pronounced for 

 this country, made its appearance at Sidmouth, South 

 Devon, and lasted for only five minutes. I managed 

 to secure two satisfactory photographs of it, one of 

 which is here reproduced (Eig. i). It shows clearly 



U 2 



