Beam-position monitors in the X-ray undulator beamline at PETRA

At the 12 GeV storage ring PETRA, the first synchrotron radiation beamline uses a 4 m-long undulator. The beamline, with a length of 130 m between source and sample, delivers hard X-ray photons usable up to 300 keV. The photon beam has a total power of 7 kW. Combined with the high brilliance, the powerful beam is very critical for all beamline components. Copper, located at a distance of 26 m, hit by the full undulator beam, melts within 20 ms. Different monitors are described for stable, safe and reliable operation of beam and experiments.

The kinetics of hæmoglobin.—II. The velocity with which oxygen dissociates from its combination with hæmoglobin

The velocity with which oxygen combines with, and is dissociated from, hæmoglobin is a matter of considerable interest both to the physiologist and the physical chemist; to the former because of the all-important part performed by this compound in respiration, and to the latter because hæmoglobin is an almost unique example of a large complex protein molecule which combines with gases, apparently not by adsorption, but in a simple chemical manner defined by the laws of mass action. There were several preliminary problems which it was necessary for us to solve, before our main experimental investigation could be commenced. Our first major problem was to find some very sudden method of upsetting the chemical equilibrium subsisting between oxygen, hæmoglobin and oxyhæmoglobin in solution. The time taken to upset the equilibrium must be very much shorter than the time taken by the system to regain chemical equilibrium. This problem in the case of the reaction CO+O 2 Hb⇄O,+COHb was solved by exposing the solution to a powerful beam of light; the latter caused a new position of equilibrium to be taken up, and this could be instantaneously upset by a sudden interruption of the beam of light. The system thereupon returned to its position of dark equilibrium. In order that all parts of the solution shall be passing through the same stages of the resulting reaction it is necessary that the time taken for the equilibrium to be disturbed be of negligible duration compared with that taken for equilibrium to be regained. Unfortunately, a similar method was not open to us in the present case, for the reaction O 2 + Hb ⇄ O 2 Hb is not appreciably, if at all, affected by a powerful beam of light. The factors upon which the equilibrium of this system depends have been very thoroughly studied by Barcroft and his co-workers in recent years (18) ; the principal ones are the temperature, the hydrogen ion concentration and salt content of the solution. Calculations showed that even if we had some very sudden method of changing one or more of these factors, the amount by which the system would be displaced would be too small compared with the experimental error of the quantitative methods available. The plan which we have therefore adopted was to prepare a hæmoglobin solution I and another solution II such that if I and II are very rapidly, but completely , mixed, the solution immediately after mixing is not in chemical equilibrium, but reaches equilibrium after an interval of time which is long in comparison with the time taken up by the process of mixing. Thus as an example we may mention that, in studying the rate of oxidation of hæmoglobin, solution I consisted of dilute reduced hæmoglobin, whilst solution II consisted of water containing sufficient dissolved O 2 to combine with the hæmoglobin of I. At the instant after the very rapid mixing of I and II the hæmoglobin is still partially reduced, and by methods to be described later the rate at which it subsequently becomes fully oxidised is measured. For this plan to be successful it was necessary to devise a special type of mixing apparatus, the description and testing of which have already been described in one of our previous papers (2).

II. Experiments concerning the evolution of life from lifeless matter

The work already accomplished, and the arguments adduced both in favour of and contradictory to the theory of spontaneous generation, have been so frequently under discussion of late, that it is needless to enter on a review of them. Furthermore, the question is one in which verbal argument is of little value compared with experimental evidence. On June 30th, 1870, there appeared in 'Nature' a paper by Dr. Bastian, entitled “Facts and Reasonings concerning the heterogeneous evolution of Living Things;” the perusal of this, and its continuation, led to the belief that another interpretation might be put on the results obtained by Schwann, Pasteur, and others, not so much by virtue of the arguments made use of, as by accounts of experiments given in detail. The most remarkable case was that of Exp. 19, in which the author gave a drawing of a large organized mass obtained from a solution of sodium phosphate and ammonia tartrate, which had been exposed to a temperature varying between 146° C. and 153° C. for four hours. This organism was seen to grow within the flask till it attained a certain size, beyond which it did not increase. Now a fact so distinctly stated as the production of an organism, and its development to a considerable size, from a liquid containing nothing further than phosphate of soda and tartrate of ammonia, in a flask from which the air had been most thoroughly withdrawn, and which, when containing the liquid and hermetically sealed, had been heated to so high a temperature, was (admitting the conditions and performance of the experiments to be faultless) an absolute proof of the evolution of living matter de novo . For my own satisfaction, I determined to commence a series of careful experiments, in some cases adhering strictly to the conditions of those made by Dr. Bastian; but it was necessary to devise some refinement on the mode of examining the liquids experimented on without exposure to atmospheric air; the means for accomplishing this I will now describe. The most promising plan seemed to be, to open the sealed vessels in an atmosphere artificially prepared so as to be free of living matter. Hydrogen being fourteen times lighter than common air, may remain in contact with it without risk of contamination by floating matter; indeed Prof. Tyndall’s demonstration, by means of a powerful beam of light, that such an atmosphere is free from dust, was sufficient to warrant its use. The means whereby this fact was made of further practical value are the following.